User:Tpoas/沙盒

基础备份。

古典晚期罗马军队
君士坦丁大帝的拉布兰旗
存在時期	公元284年至480年 (西部) 或者是公元640年(东部)
國家或地區	罗马帝国
部門	军队
規模	大约在400,000–600,000左右
建制的单位类型	御林军, 罗马中央军, 罗马野战军, 罗马边防军, 蛮盟佣兵
參與戰役	萨塔拉之战 (298), 斯特拉斯堡战役 (357), 泰西封战役 (363), 亚德里安堡战役 (378) 和沙隆战役 (451)

在Venice圣马可圣殿宗主教座堂反映四帝共治制的雕塑时期斑岩雕塑, 图中显示了戴克里先和他的三位同僚。在左边的是戴克里先和马克西米安,东西的两位奥古斯都，即正皇帝; 在右边的这是伽列里乌斯和君士坦提乌斯一世,两位凯撒，即副皇帝.请注意由于多瑙河伊利里亚人军官习俗的影响，古典晚期军官们普遍带着羊毛制的潘诺尼亚帽（作战用），以及带着鹰头剑柄的长剑

在现代学术中, 古典晚期罗马军队说法始于284年即位的戴克里先,并于476年随着罗慕路斯·奥古斯都的废位而结束, 囊括了整个西帝国的多米那特制统治时期. 在395-476期间，罗马帝国西半部的军队逐渐解体, 而东帝国,或者被称为东罗马军队 (或早期的拜占庭军队) 在规模和结构上基本保持完整，一直持续到查士丁尼统治的结束(公元527-565年).

元首制军队(30 BC – 284 AD)由于混乱的3世纪而经历了重大变革. 与元首制部队不同，4世纪的军队严重依赖征兵其士兵的报酬远低于2世纪。 来自帝国以外的蛮族提供了比第一/二世纪军队更高比例的新兵,但几乎没有证据表明这对军队的作战表现产生了不利影响。

学术上对4世纪军队规模的估计差异很大，范围从大约400,000到超过100万不等（与2世纪时期规模相似，或者大2至3倍）. 这是由于当时的参考依据过于碎片化，不像2世纪军队拥有完整的记录文档。

在四帝共治下,与地方总督军政合一的元首制不同，新制度是军政分离的。

与2世纪军队相比，罗马军队结构上的主要变化是建立了规模庞大的常规卫戍部队(comitatus praesentales), 作为精锐的中央军，其规模在2万至3万之间。他们通常驻扎于京畿: (东部是君士坦丁堡, 而西部则是米兰)，因此远离帝国的边疆。这些军队的主要功能是阻止 皇位的觊觎者, 通常由皇帝亲自指挥。军团 被分成较小的单位，规模与元首制的辅助军团相当。步兵 采用了比元首制军队的骑兵更具保护性的装备。

与元首制的军队相比，骑兵在后期军队中的作用似乎没有明显的加强。有证据表明，骑兵与二世纪时期的人数和比例大致相同，其战术角色和声望仍然相似。 然而，晚期罗马军队的骑兵 衍生出更加专一化功能的单位, 例如(甲胄冲击骑兵和具装冲击骑兵) 和弓骑兵。在4世纪后期，骑兵因其在三场重大战役中的糟糕表现而获得无能和怯懦的声誉。相比之下，步兵保持其传统的卓越声誉。

3世纪和4世纪，许多现有的边境堡垒得到了升级，使它们更具防御性，并建造了具有更强防御能力的新堡垒。对这一趋势的解释引发了一场持续的争论，即军队是采用了 纵深防御战略 还是继续采用与早期元首制相同的“前瞻性防御”姿态。 后期军队防御姿态的许多因素与前线防御相似，例如位于前沿位置的堡垒，频繁的跨境行动以及同盟蛮族部落以作为外部缓冲区。无论防御策略如何，它在防止日耳曼蛮族的入侵方面显然不如1世纪和2世纪那么成功。这可能是由于蛮族在边境的压力愈发加强，或者是为了将战斗力最强的部队留在中央而使边防部队得不到足够的支持所导致的。

古典晚期罗马帝国军队的起源

我们关于4世纪军队部署的大部分证据都包含在一份文件中，即 罗马百官志,记录了395-420期间罗马所有公共事务官员（军事民政都囊括在内）的手册。百官志的主要缺点是它缺乏任何人员数据，以以至于无法估计军队规模。它也是在4世纪末编制的;因此很难确定之前时间点的情况。然而，由于缺乏其他证据，百官志仍然是军队结构的核心来源。 百官志也遭受了严重的资料缺失，并且在几个世纪的誊写抄录中使得中间的问题激增。

4世纪军队的主要文学来源是阿米安努斯所撰写的Res Gestae《历史》,其幸存的书籍涵盖353至378年期间的罗马军队。玛尔切利努斯本人是一名资深士兵，被学者视为可靠和宝贵的资源。但他在很大程度上无法弥补百官志在军队单位以及实力方面的数据缺失，因为他很少有具体数字在内。第三个主要来源是5至6世纪之间在东罗马帝国下达的帝国法令的集合: 狄奥多西法典 (438)和民法大全 (528–39)。这些罗马法律的汇编可以追溯到公元4世纪，其中包含许多与晚期帝国军队内对督查和管理的各类法规。

De re militari,即《军事论》, 由4世纪晚期或5世纪初的作家维盖提乌斯斯撰写,其中包含有关晚期帝国军队的大量信息，尽管其重点全在共和制和元首制时期的军队上。然而，维吉蒂乌斯严重缺乏军事经验导致写出来的东西极不可靠。例如，他说军队在4世纪晚期放弃了盔甲和头盔（他提供荒谬的解释，声称这些装备太重了），这与雕塑和其他艺术上的证据相矛盾。 一般来说，他的说法太过于天马行空，除非能够得到其他史料的证实。

与1世纪和2世纪相比，古典晚期帝国军队的研究者们必须面对3世纪之后关于军队的相关记录严重缺失的问题。因为203年之后帝国不再向役满到期的辅助军团士兵发放证书 （因为来自于卡拉卡拉的“善意”当时几乎所有人都已经是罗马公民）。此外，罗马军人的墓碑,祭坛和其他神殿的数量大幅减少。建筑材料（例如大理石砖上）上带有军队士兵们的浮雕的现象也趋于绝迹。 但这种趋势不应被视为军队在行政管理上走向简单粗暴。来自埃及的莎草纸文稿证据表明，军队在4世纪仍保留详细的书面记录（其中大部分由于有机物分解而丢失）。最有可能的是，石制碑文的减少是由于当时风俗的变化，比如说受到蛮族兵员增加和兴起的基督教的影响。 石制碑文的缺乏给我们对晚期罗马帝国的军队的研究留下了严重的史料缺失，并使得许多结论无法被确定。

A.H.M. Jones所著的The Later Roman Empire, 284-602 (LRE)开创了全新的关于现代对古典晚期罗马军队的研究 . 这本1964年出版的书因为其丰富的细节和文献资料至今仍然是学者们极为重要的研究材料。当然这本书的问题在于其年代久远，在出版之后的数十年间学术界已经出现了大量的考古工作以及相关的研究。

四世纪军队的发展

一切的基础：元首制时期的罗马军队

元首制正规军由其创始人奥古斯都 (30 BC – 14 AD在位)建立并使之保留至3世纪末。 正规军由两种不同的军团组成，两个军团主要依靠募兵。

作为精英的罗马军团是大型步兵编队，数量在25到33之间。每个军团有5,500名兵员（所有步兵军团都保留了一支120人规模的小型骑兵部队）只招收罗马公民. 辅助兵团 由大约400个更小的单位（大队）组成。每个大队500人（少数可达1000人）,分为大约100队骑兵，100队步兵和200队混合骑兵/步兵部队或者同规模部队。 一些辅助军团被指定为“弓兵团”,这意味着它们专门用于对敌弓箭射击。 因此，辅助军团几乎包含了所有罗马军队的骑兵和弓箭手，以及（从1世纪后期开始）与军团大致相同数量的步兵。辅助步兵主要在自由民'内招募，': 那些没有公民权的非奴隶罗马住民，但是同时也接收罗马公民和住在帝国境外的巴巴里/蛮族。 在那段时期，罗马军团和辅助军团几乎都部署在边境省份。 能直属于皇帝并被皇帝在短时间内快速集结指挥的只有10000人左右的精英罗马禁卫军。

直到公元3世纪，军队的高级军官几乎都来自于意大利贵族。这些贵族被分为两类，一类是正式的有身份的世袭贵族 (ordo senatorius), 由罗马元老院的600名成员和他们的儿孙组成，以及数以千计的罗马骑士们.

世袭元老和罗马骑士将军政服役结合，组成了具有罗马特色的晋升体系, 通常从罗马的一个初级行政职位开始，随后在军队中任职5至10年，最后在罗马或者各个行省担任高阶职务。 这个由不到一万人所组成的小型，紧密结合的统治寡头集团在8000万居民的帝国中垄断了政治，军事和经济权力，并成功地稳定了整个帝国。 在其存在的最初200年(公元前30年 – 公元180年), 帝国只遭受了一次重大内乱(即四帝之年).其余时间极少数图谋不轨的行省总督的僭越行为都会被迅速镇压。

在军中，世袭贵族 (senatorii)通常担任以下职位：

(a) legatus Augusti pro praetore(边境行省的总督，他是部署在那里的军队的总司令，也同时是该地区民政部门的负责人)

(b) legatus legionis(罗马军团长)

(c) tribunus militum laticlavius (罗马副军团长)。

罗马骑士通常担任以下职位:

(a) 埃及和一些非重要行省的总督

(b) praefecti praetorio (罗马禁卫军的指挥官，仅两位)

(c) praefectus castrorum (军团内的宿营长，军团内的三把手)及军团内其余的五名tribuni militum (军事保民官，高级参谋军官)

(d) 辅助军团的指挥官praefecti

到了1世纪末，帝国内形成了一个特别的由非意大利人的军人所组成的罗马骑士阶层，肇因起源于皇帝在他每一年执政结束时将每个军团的primuspilus （首席百夫长）提升到骑士等级。这会使大约30名职业军人，大多数是非意大利人，加入贵族阶层。 他们要比意大利的同僚们贫穷得多，毕竟这些意大利的同僚很多都仰赖于他们所凭依的家族。 其中突出的是罗马化的伊利里亚人,是居住在帝国境内各省，例如潘诺尼亚 (今匈牙利/克罗地亚/斯洛文尼亚), 达尔马提亚 (今克罗地亚/波斯尼亚)和 上默西亚 的(今塞尔维亚)伊利里亚语部落的后裔,以及邻近的[默西亞 (羅馬行省)|下默西亚]] (保加利亚北部)和马其顿 行省居住的色雷斯人。从图密善时期(81–96在位)开始, 当超过一半的罗马军队部署在多瑙河地区时，伊利里亚和色雷斯省成为最重要的辅助兵团募兵基地，后来也成为罗马军团的最重要的兵员来源。

三世纪时期的发展

图中是一位穿着典型的3世纪末步兵装备的古罗马军装爱好者。头盔是Niederbieber式样, 盔内侧顶部有交叉状的加强金属脊,可以使护颊被扣在一起. 剑则是 罗马长剑 (长度在 900 毫米/36 英寸上下), 在一至二世纪只有罗马骑兵才会使用。这名士兵携带着 spiculum, 是一种罗马重型标枪. 他还装备着被称为 (lorica hamata的锁子甲)，还拿着椭圆形的盾牌。 他的服装则包括了长袖的丘尼卡，长裤以及靴子。四世纪的步兵装备与三世纪的非常相似, 但是重型标枪已经被另一种重型穿刺标枪(hasta)所替代，而头盔则被"Intercisa样式的头盔所代替。".

罗马边境城市杜拉欧罗普斯的湿壁画，时代可以追溯至公元250年. 中央是未穿装备的轻骑兵在发起冲锋, 上下则是步兵在使用罗马长剑作战; 他们穿着及膝长的鳞甲，有些甚至包括双臂。

3世纪初军队的开创性发展是由 卡拉卡拉皇帝（211-18在位）颁布的212年的安东尼努斯敕令所带来。这赋予了帝国所有自由居民罗马公民身份，结束了无公民权自由民的二等地位。 这条法令打破了罗马公民的罗马军团和自由民组成的辅助军团之间的区别。在1世纪和2世纪，军团是意大利“宗主国”在其藩属中占主导地位的象征（和担保人）。在3世纪，他们不再在社会上优于那些外来者们（尽管他们可能在军事方面保留了他们的精英地位），同时军团特殊的盔甲和装备(比如说 罗马环片甲)也被逐步淘汰。

因为意大利世袭贵族在军队中的高层逐渐被出身于自由民的前头等百夫长所取代，高级文职和军职之间交替任职的传统晋升体系在2到3世纪的交际于是被逐渐废弃。.在公元3世纪，只有10％的辅助军团的长官来自于意大利的罗马骑士，而前两个世纪的比例则是大多数。 与此同时，垄断军方上层的世袭贵族也被罗马骑士所取代。塞普蒂米乌斯·塞维鲁 (197至211年间在位) 任命了三个出身于自由民的首席百夫长作为他所组建的三支新军团的新长官，而加里恩努斯 (260–68)对所有其他军团也如法炮制, 给予他们praefectus pro legato ("代行军团长官")的头衔. 这些新晋的罗马骑士团体的崛起为军队提供了更专业的将领，但却促进了雄心勃勃的将军的军事叛乱的概率。 3世纪发生了无数次政变和内战。很少有3世纪的皇帝能长留帝位或是寿终正寝。

皇帝对频繁产生的不安全状况迅速做出了回应，他们逐渐建立了一支可以快速集结的部队。这些被称为 扈从军 (原意"护卫", 之后衍生出英文单词"committee"，即委员会). 除了帝国禁卫军的10,000名成员，塞普蒂米乌斯·塞维鲁还设立了第二帕提亚军团. 驻扎在罗马附近的阿尔巴诺拉齐亚莱 , 这是自奥古斯都以来第一支驻扎在意大利的军团。他从边境驻扎的骑兵队里调剂人员，将equites singulares Augusti, 即帝国护卫骑兵的数量增加了一倍，使数量增加到了2000人。 他的扈从军规模因此达到了17000人，相当于31个步兵大队和11个骑兵大队。 之后的皇帝们一直采取强化中央军的政策，这个趋势在君士坦丁一世(312–337年在位)，他的扈从军规模可能已有10万人，达到了军队总数的四分之一。

在加里恩努斯统治时期，一些高级军官被他任命为 督军 (复数形式: duces, 即中世纪公爵的起源), 以指挥所有的护卫骑兵。军队内包括了equites promoti (从军团中分离的骑兵支队),以及伊利里亚轻骑兵(equites Dalmatarum)和盟邦蛮族骑兵(equites foederati). 在君士坦丁一世的统治下，骑兵的长官被封予骑兵长官的头衔（magister equitum）magister equitum, 在共和国时期这一职责由狄克推多的副手担任. 但根据过去的学者们所描述，早期这个职位并未暗示那个时期有过一支独立的纯骑兵军队的存在。两名骑兵长官麾下的军队混有步兵和骑兵，而且仍以步兵为主。

3世纪军团的规模逐渐缩小，甚至还有一些辅助单位夹杂其中。军团被分解成较小的单位，这可以通过在英国遗留下来的传统大型基地遗址来证明，他们的规模随着时间逐渐缩小，最终被放弃使用。 此外，从2世纪开始，一些从母单位内被分离出来的子单位最终形成了新的作战单位， 例如2世纪初位于达契亚的伊利里亚骑兵分队vexillatio equitum Illyricorum和驻扎在英国的equites promoti与numerus Hnaufridi。 这导致了4世纪各种新单位类型的衍生,这些作战单位的规模通常少于元首制时期的军队建制。 例如，在2世纪， 布旗队vexillatio (衍生自 vexillum 即"军旗"之意) 是从罗马军团/辅助军团分离出的部队单位，既可以是步兵也可以是骑兵。而在公元4世纪，它通常作为精英骑兵团的建制出现。

从3世纪开始军队内开始有记录出现以蛮族部落的名字命名的正规小型部队单位 (而不是以自由民部落的名字为名). 这些部队是蛮盟佣兵foederati (对罗马有军事义务的盟军)转化过来的正式部队建制,这一趋势将在4世纪越发明显。 驻扎在不列颠的第一萨尔马提亚骑兵大队, 可能是由马可·奥勒留在175年送去驻扎哈德良长城的5,500名萨尔马提亚骑兵俘虏中的一部分组成的。 当然至少在公元3世纪时期，还没有史料充分证明非常规建制的蛮族民兵部队成为了元首制时期罗马军队的一部分。

三世纪危机

(左侧跪着的)瓦勒良被 （穿着盔甲的）萨珊沙阿 沙普尔一世在259年的埃德萨之战中俘虏后跪着求饶 , 这是帝国在3世纪后期遭受的最屈辱的军事灾难。该岩石浮雕 位于设拉子附近地区Naqsh-e Rostam

3世纪中叶，帝国陷入极为严重的军事和经济危机 251-271的一系列军事上的灾难表现使得高卢，阿尔卑斯地区和意大利，巴尔干半岛和东方地区被阿勒曼人，萨尔马提亚人，哥特人和波斯人占领，几乎导致帝国解体。 与此同时，罗马军队还要努力应对毁灭性瘟疫的影响,现在该流行病被认为是天花, 251年始于塞浦路斯的塞浦路斯大瘟疫，并且在270年时仍然在肆虐,还可能带走了克劳狄二世 皇帝的性命(268–270年间在位). 而根据二世纪后期安敦尼疫病爆发时期所遗留下来的史料来看，极有可能就是天花，当时帝国内15%-30%的居民因此病歿。 根据佐西穆斯的记载，实际情况可能远糟于此。 军队以及他们所居住的（同时主要是招募的来源地）边境省份，因为他们人员集中且被频繁调动，使得这些地区成为了瘟疫的重灾区

3世纪的危机开始了社会经济影响的连锁反应，这对古典晚期军队的发展具有决定性作用。由于瘟疫造成的严重破坏和税基锐减的二者结合使得帝国政府破产，帝国中央决定生产大量成色低下的货币，比如安东尼尼安努斯,作为作为当时支付帝国军队薪水的银币, 在215年到该世纪的60年代的数十年里成色降低了95%. 即使用相同质量的贵金属可以制作20倍的硬币。 这导致价格疯狂通胀：例如，戴克里先的小麦价格是元首制时期的67倍。 货币经济崩溃，军队不得不依靠征收食品换取补给以维持。 军队征税毫无公平可言，使得他们所驻扎的边境省份遭到毁灭性的打击。 士兵的薪水毫无价值可言，这使得军队的新兵减少到仅能维持军队建制存在的水平。 这样的状况使得境内的公民不愿从军，帝国政府被迫使用强制征兵的手段 而同时因为瘟疫又减少了大量的人口，帝国不得不大量招募蛮族进入军队。到4世纪中叶，蛮族兵员达到了新兵总数的四分之一（精英军团内甚至超过三分之一），比1世纪和2世纪的比例都要高得多。

多瑙河军官团

由奥勒良270年在罗马修建的奥勒良城墙。这是自公元前650年在高卢人洗劫罗马而建造塞维安城墙之后的第一座新城墙,它象征着3世纪时期帝国各处都存在的不安感。原始高度: 8米 (25 英尺). 之后在410罗马被洗劫后增高到16米 (52 英尺)。 城墙和塔楼本都有圆形的城垛,不过只有极少部分留了下来，至今只有19公里留存

到了公元3世纪，罗马化的伊利里亚人和色雷斯人, 大多来自罗马骑士们及他们的后代,垄断了军队的高级官员位置。 直到最后，多瑙河军事高官们夺取了对国家本身的控制权。268年加里恩努斯 (260–268年间在位) 被伊利里亚和达契亚的高级军官组织的政变推翻,其中包括了他的继任者克劳狄二世和奥勒良 (270–275年间在位). 以及他们的继任者普罗布斯 (276–282年间在位)，戴克里先 (284–305年间在位)以及四帝共治的同僚们组成的永久性的军政府。他们可以是出生在同一个省,(有些甚至出生在同一个城市,比如上默西亚的军队驻地西尔米乌姆)的老乡们,或者是曾在同一军团中服役的同僚们。

奥勒良即位后军政府用一连串的胜利扭转了251-71的军事灾难，其中最为出名的的是克劳狄二世在纳伊苏斯战役 战胜了规模极为庞大的哥特人部队, 这对哥特人打击甚大，以至于哥特人直到一个世纪之后的亚德里安堡战役 (378)之后才再次严重威胁帝国。

伊利里亚皇帝或多瑙河皇帝特别关注在危机期间由于瘟疫和野蛮入侵造成的边境省份人口减少现象，因为这个问题在他们自己所在的多瑙河省份尤其严重。 因为缺乏人力，这些省份的耕地大量荒废。 因此，为了应对人口减少对军队招募和供应构成的严重威胁，伊利里亚军政府采取了一项积极的政策，将被击败的蛮族部落居民大规模地重新安置在帝国领土上。 奥勒良在272年将大量卡尔皮人迁了潘诺尼亚。 (此外，到275年，他撤销了达契亚省, 将整个省人口迁移到了默西亚，动机与之前相同). 记录档上有记载提到他的继任者普罗布斯在279、280年将100,000名 巴斯塔奈人以及后来还有相当数量的格皮德人, 哥特人和萨尔马提亚人迁移至默西亚. 戴克里先之后持续地执行这项政策，根据维克多的记载，他转移了297个大量的巴斯塔奈，萨尔马提亚和卡尔皮的部落到边境省份。 虽然这些人在帝国定居的确切条件未知（说法多种多样），但共同特征是给予蛮族土地换来的就是兵役或者远高于其他省份份额的征兵名额。从罗马政府的角度来看，这项政策有三重好处，即削弱敌对部落，重建受瘟疫蹂躏的边境省份（将其废弃的田地重新养护起来）并为军队提供一流的新兵。这也受到了蛮族囚犯的欢迎，他们对帝国可能会给予他们土地的政策感到高兴。在4世纪，这些蛮族群体被称为军户.

伊利里亚王朝出的皇帝统治帝国一个多世纪，直到379年才结束。事实上，直到363年，权力都一直由当初建立军政团体的成员后代所掌握。君士坦丁一世的父亲君士坦提乌斯在戴克里先的四帝共治政府中任职凯撒（西部的副皇帝）. 君士坦丁的孙子尤利安统治到363年。这些皇帝将军队成功地恢复到危机前的实力，但他们也只关心军队的需要和利益。他们也与拥有帝国的大部分土地的富裕罗马元老们的家族脱节。这反过来又在罗马贵族中产生了一种与军队疏远的感觉，这种感觉使得从4世纪后期元老们开始抵制军队对帝国的无止境兵员和物资需求。

戴克里先

戴克里先 (284–305年间在位)对罗马军队和政府都做了大范围的改革，这是其年间发行的铜币福利斯

戴克里先被公认为最伟大的伊利里亚人皇帝。 戴克里先大规模在行政，经济和军事施行的改革旨在为军队提供足够的人力，物资和军事基础设施。 用一位历史学家的话来说, "戴克里先......把整个帝国变成了一个有条不紊的后勤基地" (用以为军队提供补给)。

戴克里先时期的军事指挥结构

戴克里先的行政改革的双重目标是确保政治稳定，并提供必要的官僚和基础设施，以提高军队所需的新兵和兵役。在最高层，戴克里先设立了四帝共治制。这将帝国划分为两个部分，东部和西部，每个部分由奥古斯都（皇帝）统治。每个奥古斯都将依次任命一名名为凯撒的副手，他将作为他的执政伙伴（每个人都被分配到帝国的四分之一）并指定继任者。因此，这个四人小组可以灵活地应对多重和同时的挑战，并提供合法的继承。当然后者未能实现目标，在3世纪由于多次篡位而造成的灾难性内战仍然在四世纪重演。实际上，如果为每个篡位者提供潜在的大量的护卫部队来强制执行他的主张，情况可能会变得更糟。戴克里先自己退休后就眼睁睁地看到他的继任者为了权力而互相争斗。但是，将帝国划分为东西两半，同时认识到地理和文化现实，被证明是持久的；东西分治仍然使得帝国为一整体，不过在395之后便成为永久性的分裂。

戴克里先改革了省政府，建立了一个三层的省级层级，取代了以前的单层结构。最初的42个省份的数量几乎增加了两倍，大约在120上下。 这些省份归属于12个区域，被称为管区,每个管区都有一名代理官, 然后再归属于4个近卫大区, 以对应于分配给四位君主（凯撒和奥古斯都）的辖区, 每个领土都由一名近卫司政官 (请勿与具有相同头衔的罗马禁卫军长官的名称混淆)。级政府这种分割的目的是通过减少他们各自控制的力量来减少地方总督军事反叛的可能性。

此外，为了提供更专业的军事领导，戴克里先将军队体系从行省的民政机构中分离出来。边境省份的省长被剥夺了驻扎在那里的部队的指挥权，转而将这全力交给称为 duces limitis ("边防督军")，在戴克里先时期可能任命了大约20个边境督军。 大多数的督军只指挥一个省份的驻军，但少数几个督军控制了超过一个省份的督军，例如第一潘诺尼亚和诺里奇行省督军,即dux Pannoniae I et Norici. 然而，在更高的层次上，军事和行政指挥仍然统一在管区代理官和近卫司政官名下. 此外，戴克里先还完成了对元老院阶级的排挤，元老院阶级仍以意大利贵族为主导，除意大利外，元老院贵族不得担任一切高级军事指挥和最高行政职务。

人力

为确保军队获得足够的新兵，戴克里先施行了自[[罗马共和国|罗马共和国]时代以来首次对罗马公民进行系统的年度征兵制度。此外他可能颁发了一道最早记载于313年的法令，强制正在服役的士兵和退伍军人的子弟入伍。

戴克里先时期，军团的数量，可能还有其他军事单位建制，增加了一倍多。 都增加了一倍多。 但军队的总体规模不可能增加得那么多，因为单位兵力似乎减少了，在某些情况下还大大减少了。例如军团编制，相比于元首制时期的5500人规模，戴克里先的新军团只有1000人。也就是说，新军团可能只增加了军团总人数的15%左右。 即便如此，学者们普遍认为戴克里先大幅增加了军队人数，至少增加了33%。

补给

戴克里先主要关注的是将向军队提供粮食供应置于合理和可持续的基础上。为此，皇帝结束了对军队能够任意在当地征收粮食税(indictiones)的权利， 因为军队的负担主要落在边疆各省，这样做会毁了当地的经济。他建立了一种每年定期征税 indictiones ("税款征收")的制度,要求征收的税款预先设定为5年，并与各省的耕地数量有关，并以全帝国范围内的土地、农民和牲畜的彻底普查为后盾。 为了解决某些地区农村人口减少的问题（以及随之而来的粮食减产），他下令在元首制时期可以自由迁徙的农民们，绝不能离开他们在普查中所登记的地方(法律术语称'origo'). 这项措施将佃民及其后代捆绑在了他们的地主的庄园内。

军事基础设施

在恢复军队规模的同时，戴克里先的努力和资源集中在沿着帝国所有边界的防御基础设施进行大规模升级改造，包括新建堡垒和战略性军用道路。

君士坦丁一世

君士坦丁一世 (312–337年在位),有史以来第一位建立了大规模的扈从军 (帝国护卫军)并将军队分为野战军(comitatenses)和边防军(limitanei) ,使罗马后期的军队产生了百官志中所描述的结构. 图为卡比托利欧博物馆所展出的君士坦丁胸像的一部分

在312年击败马克森提乌斯后,君士坦丁解散了罗马禁卫军,结束了后者长达300年的存在。虽然当时的原因是禁卫军支持他的竞争对手马克森提乌斯，但因为皇帝现在很少居住在罗马，驻扎在那儿的军队也就毫无意义了。原先护卫皇帝的禁军骑兵,equites singulares Augusti,即罗马禁卫军附属骑兵队,也就被御林军所取代。这些精锐的骑兵团在君士坦丁即位时便存在，可能是由戴克里先创立的。

君士坦丁将他的护卫军队拓展成一支占有永久主导地位的军事力量。他将边境的部分军力回收并创建了两支新的部队：更多的骑兵单位"布旗队"和步兵单位"辅助步兵团"。扩大规模后的扈从军由两名新军官指挥,一位步军长官负责所有的步兵部队,一位骑兵长官负责骑兵部队。扈从军被正式命名为野战军 以区别于(边防军). 君士坦丁的扈从军规模不详，但根据佐西穆斯的说法，君士坦丁在对马克森提乌斯的战争中动员了98,000名士兵。 很有可能军队中的大多数士兵都直接来于他的扈从军. 如果接受君士坦丁军队人数约为40万的说法，那么这些士兵约占正规军总数的四分之一。 当世学者们一直在讨论为何君士坦丁要保留如此庞大规模的扈从军，一般传统观点认为，君士坦丁将其认作一种战略储备以用于对抗大规模入侵帝国腹地的蛮族军队，或者作为跨越边界征讨蛮族的大型远征军的主力。但更多的近代学者则认为其主要功能是为了防止潜在的篡位者而做的保险措施。 (请参照下面会论及的古典晚期罗马军队的战略).

君士坦丁一世完成了军事机构与行政结构的分离。管区代理官和近卫司政官失去了他们的战地指挥权，成为了纯粹的行政官员。然而他们在军队事务中发挥了核心作用，因为他们仍然负责部队兵员招募，军饷以及最重要的提供补给。 但是当时的边区督军究竟是直接汇报给皇帝，还是扈从军的两位长官，到现在仍然未知。

此外，君士坦丁似乎重新组织了多瑙河沿岸的边防部队，分别用新的骑兵连“cunei”和辅助军团“auxilia”代替原来的骑兵大队“alae”和步兵大队“cohortes” 目前还不清楚新式部队与旧式部队有何不同，但驻扎在边境的部队 (相比于扈从军内的建制)要小上许多,只为原来的一半左右。 但除了多瑙河/伊利里亚以外的地区还是得以保留了旧的建制。

5世纪的历史学家佐西穆斯强烈批评他建立过于庞大的扈从军的做法,指责君士坦丁破坏了他的前任戴克里先的加强边防的工作: "由于戴克里先的远见卓识，罗马帝国的边境到处都是城市、堡垒和塔楼... 整个军队都驻扎在边境，所以蛮族不可能突破...但君士坦丁把大部分军队从边境撤走，驻扎在不需要保护的城市里，从而毁掉了这一防御体系。" 佐西穆斯的批评可能是过分的，因为在戴克里先时代扈从军就已经存在，君士坦丁做的无非是为了扩张扈从军组建了全新的军团并合并了旧有的建制 然而君士坦丁的扈从军的主要来源便是从边境调动回来的边防军人们 撤回大批的边防部队的行为终究还是提高了蛮族大规模突破边境进入帝国腹地的风险。

四世纪后期

随着337年君士坦丁的去世,他的三个儿子君士坦丁二世, 君士坦斯一世 and 君士坦提乌斯二世,将帝国三分，分别统治西部（高卢，英国和西班牙），中部（意大利，非洲和巴尔干半岛）和东部。他们每个人都接收了他们父亲的扈从军的一部分.到了353年，只有君士坦提乌斯存活下来, 但这三支扈从军永久性地驻扎了下来，分别在高卢，伊利里亚和东部。 到了四世纪六十年代，边境督军都直接向当地的中央扈从军长官直接汇报工作。 然而除了地区性的扈从军外, 君士坦提乌斯还保留了一支随时可动用的部队, 被称之为 常备扈从军 (Comitatus Praesentalis). 而三个扈从军所在的地区的扈从军的数量却在不断增加,直到百官志 ( 约公元400年),西部有6支野战军，而东部则有3支。 这些对应于西部的边境管区,在西部则对应不列颠，三部高卢（阿基坦高卢，卢格敦高卢和比利时高卢）,伊利里亚西部(潘诺尼亚),阿非利加和西班牙; 在东部则对应着: 伊利里亚东部(达契亚), 色雷斯和东方。相对的扈从军指挥官开始对口于行政部门的长官管区代理官,控制着管区内的所有部队,其中包括了边区督军.因此，在这一时间点上，平行的军事/民事行政结构可归纳如下：

395年古典晚期罗马帝国的行省行政结构

层级	军事长官	民政长官
行省	边区督军	督查官
管区	大元帅 (东部)/野战军司令 (西部)	管区代理官
近卫大区	奥古斯都/凯撒	近卫司政官

区域性的扈从军的产生是对君士坦丁强干政策的部分逆转，实际上证明了佐西穆斯对君士坦丁批判,边防军 缺乏中央对此的有效支持。

尽管地区性的扈从军数量激增,不过帝国中央的扈从军仍然存在,在百官志撰写时期有三支常备扈从军的存在, 每支定员20000-30000上下,总计仍有75000人. 如果接受当时军队人数约为35万的说法,扈从军仍占总军队规模的20-25%。不晚于365年且仍然能留在扈从军中的军事单位,一概被统称为中央军 (直译为"来自宫中), 是所谓野战军的高级形式。 于是军队内的部队单位被分为四个等级,代表着不同的质量,声望与薪酬。以降序排列的话便是御林军, 中央军, 野战军和边防军。

军队规模

由于当时留存相当多详细可究的证据，现代学者对公元1世纪和2世纪罗马军队的规模有广泛的学术共识。然而，关于4世纪陆军的规模，众人对此莫衷一是。由于缺乏关于编制人数的证据，导致对陆军后期力量的估计大相径庭， 范围从约400000 (与2世纪大致相同)到100万以上。 主流学者主要分歧在于有些人认为实际是400000的"较低值"以及600000的较高值。

庞大的军队规模假说

一些传统的学者观点认为，4世纪的军队比2世纪的军队大得多，规模应该是原来的两倍。6世纪后期的作家阿伽提乌斯给出了645,000的数字，推测是君士坦丁一世时期的巅峰值。 这个数字可能包括舰队的海军士兵，那陆军人数大致在600,000左右。佐西穆斯将312年包括君士坦丁皇帝在内的所有皇帝的军队总数相加，于是得出了581,000的总数. A.H.M. Jones' 所撰写的古典晚期帝国 (1964), 包含了对罗马古典晚期的军队各类的基础研究,。他以自己对建制兵力的估算方法应用在百官志的所列的单位上，从而得出了600,000的总数。 (海军除外)

然而，琼斯的600,000的数字是基于对边防军人数的估算,可能远高于实际值。琼斯根据戴克里先时期使用的莎草纸所写的工资支给文件证据证明计算了埃及的建制人数。但R. Duncan-Jones对史料进行严格的重新评估后得出的结论是，琼斯的建制人数高估了2-6倍。 例如，琼斯估计边境的军团编制在3000人左右，而其他的单位大致有500人上下。 但Duncan-Jones的修订发现，边境驻扎的军团规模仅为500人, 骑兵大队只有160人，骑兵队只有80人即使考虑到其中一些单位可能是某个大单位的分队，戴克里先的单位兵力很可能远低于早期

特里高德在对拜占庭的军力考察上认可了大规模的古典晚期军队的说法。特里高德认为吕底亚的约安尼斯所给出的389,704人的数据对应的是戴克里先刚继位的285年, 佐西穆斯所给出的581,000人对应的则是312年的数据. Treadgold估计军队的规模在235-285年保持不变,在285-305年迅速增加了50%,在之后的90年间(305-395)大致保持不变

但是特里高德的分析在以下几个方面受到批评：

1. 军队规模在235和285之间保持不变的结论似乎难以置信，因为这一时期出现了三世纪危机，在此期间，塞浦路斯大瘟疫的影响,无数的内战和毁灭性的蛮族入侵严重削弱了军队的招募能力。
2. 如果吕底亚的约安尼斯给出的39万的数字如果是戴克里先刚开始统治的兵力的话，那么这个数字是值得怀疑的，根据学界的研究，这个数字更像是戴克里先扩员成功后的最高兵力。
3. 特里高德声称戴克里先将军队数量增加了50％以上，被另外一名学者希瑟认为难以置信，他指出即使增加三分之一的人力也要付出极大的努力。
4. 特里高德的估计是根据佐西穆斯提供的君士坦丁军队的数据得出的, 而佐西穆斯是一个著名的不靠谱的编年史学家 无论是在一般情况下，还是在具体数字方面：例如，他报告说，在357年的斯特拉斯堡战役中，有6万名阿勒曼尼人,相比于被当代史学家认为是可靠的马尔切利努斯所给出的6000人的数据,佐西穆斯所给的数据出现了极为明显的夸大。

小型的的军队规模假说

传统的4世纪军队规模大得多的观点在近代已经不受一些历史学家的青睐，因为现有的证据被重新评估，新的证据被发现。修正主义的观点认为，4世纪的军队在高峰期时，其规模与2世纪的军队大致相同，并且在4世纪后期大幅度缩水。 阿伽提亚斯和佐西穆斯的统计数字，如果他们的说法是有效的，那也只可能代表君士坦丁时期的官方预计，而远非实际的力量。微不足道的证据是，后期的部队往往兵力严重不足，实际也许只有官方的三分之二左右。 因此，阿嘉西亚斯在纸面上的600,000可能只不过有400,000左右。后者这个规模与六世纪的吕底亚的约安尼斯所提供的戴克里先时期除去海军水兵的军队总数389,704是吻合的。Lydus的数字比Agathias的数字更可信，因为它的精确性(它是在一份官方文件中发现的)，并且它被归于一个特定的时期[2]。 来自帝国边界所出土的考古学证据表明，晚期堡垒的设计目的是为了容纳比其过于元首制时期更少的守军。如果可以使用百官志中列出的堡垒识别此类场地，这些堡垒内部所能容纳的驻军编制人数也同期缩水。可以以戴克里先创建的Legio II Herculia, 第二赫丘利军团为例。比起元首制时期的军团驻地，堡垒只有其七分之一左右，从此可以推断这个军团大概只有750人左右。在多瑙河畔的阿布西纳（Abusina），Cohors III Brittonum，第三不列颠骑兵大队，所驻扎的堡垒只有过去图拉真时期的堡垒的十分之一大小，也由此推断这支大队只有50人左右。必须谨慎对待这些证据，因为在《百官志》中对带有地名的考古遗址的鉴定往往是试探性的，而且有关单位可能是某大单位的分队（《百官志》经常出现同一单位同时出现在两个或三个不同的地点） 不过一般来讲考古学者都从保守角度起见来估计，所以他们一般都会选择保守的角度来对边防军的军事单位规模进行估算。 因此,考古学上发现的证据表明,公元400年的时候，驻扎在不列颠的守军仅有公元200年元首制时期的三分之一（200年时期是55000人左右,400年时期只有17500上下）。

同时，更多的最新研究表明，2世纪的正规军数量比传统上预估的约30万人要高得多。这是因为2世纪的辅助军团人数不仅与1世纪初的罗马军团人数相等，甚至有的时候还会比预估的数字大上50%左右。 甚至有的时候还会比预估的数字大上50%左右。在2世纪末,元首制的军队可能达到近45万的高峰(不包括海军官兵和盟邦的佣兵)。 此外，有证据表明，2世纪部队的实际兵力通常比4世纪部队更接近官方实际数据（约85%）

对整个帝国各个时期的陆军兵力的估计可归纳如下：

公元24-420年的罗马军队规模

Army corps	提比略 24	哈德良 约130年	赛维鲁 211	戴克里先 284年开始统治时	戴克里先 305年退位时	君士坦丁一世 337年	百官志 (东部约395年，西部约420年)
罗马军团	125,000	155,000	182,000
辅助步兵	125,000	218,000	250,000
罗马近卫军	~~5,000	~~8,000	~15,000
罗马军队总数	255,000	381,000	447,000	保守估计: 260,000? 特里高德: 389,704	保守估计: 389,704 特里高德: 581,000	埃尔顿: 410,000 特里高德: 581,000	保守估计: 350,000? 特里高德: 514,500

NOTE: 仅计算常规部队: 蛮盟佣兵和（元首制时期有4-5万规模的）罗马海军不纳入计算

军队结构

4世纪军队包含三种类型的军队: (a) 常备扈从军 (comitatus praesentales)。这些通常是靠近帝国首都（西方的米兰，东方的君士坦丁堡），通常陪同皇帝对外出征。 (b) 管区扈从军 (comitatus) 这些都位于边境或附近的战略地区。 (c) 边防军 (exercitus limitanei).

类型(a)和(b)经常被定义为"机动野战军"。这是因为,与边防军单位不同的是,他们的行动不局限于一个行省。他们毕竟职责不同，这些扈从军是皇帝用来阻止帝国内潜在的篡位者的最终保险: 这样一支强大部队的存在本身就会威慑许多潜在的对手，如果没有，仅靠扈从军往往就足以打败他们. 他们的次要作用是陪同皇帝对外远征，如对外战争或击退大规模的蛮族入侵。 另外一方面,管区的扈从军负责的是在重大入侵的时候支援本地的边防军

高层的指挥架构

帝国东部的指挥结构

公元395年的东罗马军队的高层指挥架构。 指挥官和军队规模都是基于 百官志 关于东部的材料. 东部的大元帅,掌管着扈从军, 向上直接对皇帝本人负责。根据Jones和Elton的研究，督军则直接向管区所在大元帅汇报工作。所给出的地点表示这一时期军队的冬季驻扎地。

约410-425年西罗马军队的高层指挥架构。指挥官和军队规模都是基于 百官志关于西部的材料。督军和野战军司令之间的关系类似于东部督军和大元帅之间的关系,即督军直接向管区所在的高层军官负责(然而百官志把所有的军事单位全置于两军大元帅的指挥下).所给出的地点表示这一时期军队的冬季驻扎地。

百官志对于东帝国的描述要追溯于狄奥多西一世去世时的395年.此时，根据百官志的说法，在东方有2支中央扈从军 (comitatus praesentales),每支军队都是由常备军大元帅指挥, 军方的最高层的一部分，直接对皇帝负责。这两支军队都被算作是中央军。此外在东伊利里亚，色雷斯和东部三个管区还有3支扈从军,这三支军队被算作野战军。也各有一名大元帅统领, 也直接对皇帝本人负责。

帝国东部有13个边区督军直接向他们所在管区所在的大元帅负责: 伊利里亚东部(2名督军), 色雷斯管区(2), 本都管区(1), 东方管区(6)和埃及管区(2).

百官志所呈现的东帝国的军队结构直到查士丁尼统治时期 (525-565年间在位)基本保持不变。

帝国西部的指挥结构

对帝国西部的军队结构的记载的完成时间要远晚于帝国东部。大概425年的时候，西部大多地区失陷于日耳曼蛮族 然而，西部的部分在约400-425年间出现了多次修改：例如，不列颠的军队部署应该是在410年之前，因为罗马军队就是在那个时候明确从不列颠撤出的。这反映了当时的混乱，军队和指挥官的部署不断地变化，反映出了当时的需要。Heather对帝国西部军队中各单位的分析，就说明了这一时期混乱的规模。425年存在的181个扈从军的军团里，只有84个在395年之前就存在,许多 扈从军的军团也仅仅是升级的边防军单位,在395-425的30年间有76个军团在这段时间被解散，直到460年，西部军队几乎完全解体。

因此，百官志所记载的395年的西部部分并不能准确地代表西部军队的结构（相比而言东部的军事指挥体系更为准确）。

西部结构与东部大不相同。在帝国西部，395年之后，皇帝没有办法直接指挥驻扎在各个管区的扈从军的长官，这些长官们则向类似于日本幕府的将军)述职。 这种不正常的结构是由于半汪达尔血统的军事强人斯提里科(395–408掌控国政)造成的,他是狄奥多西指派作为他的儿子霍诺留的监护人,后来霍诺留继任罗马西部的皇帝。在斯提里科在408年死后,接连不断的弱小皇帝确保了这一职位的存在,成为了斯提里科的后继者的专用职位(尤其是埃提乌斯和李希梅尔),直到476年帝国西部彻底解体为止。 这个大元帅的位置一般被叫做两军大元帅 (简称为MVM, 名义上便是"两军之长官",两军则指的是骑兵和步兵). 他直接指挥着驻扎在米兰附近的单一且规模庞大的帝国西部的中央扈从军。

隶属于两军大元帅的是地方的野战军司令，他们都统领着这些地区的驻军: 高卢，不列颠，西伊利里亚，阿非利加，廷吉塔纳（今北非摩洛哥丹吉尔地区）和西班牙。与他们在东部同行不同的是, 东部的同行被称为各管区的 大元帅,西部管区的扈从军的长官都被任命为低一层级的野战军司令,只有高卢地区的高卢骑兵元帅是例外。这大概是因为除了高卢管区的扈从军之外，其余的野战军司令所指挥的士兵数目都远小于 大元帅所理应有的20,000–30,000人的规模。

根据百官志的记载, 全部的12名在西部的督军中有两位督军直接对两军大元帅而非他们所在区域的野战军司令负责。 这与东方的情况不一致，可能也不能反映395年的情况。

御林军

无论帝国的东西政府,御林军通常都作为皇帝护卫骑兵部队,游离于军队指挥系统之外。根据百官志的说法,御林军的指挥官保民官通常都对民政部门首脑国务总理大臣直接负责。 但这可能只是出于行政目的。在作战时,御林军保民官 直接向皇帝本人报告。

军队驻地

参见：Castra

野战军和边防军的部队对他们的驻扎地有不同的安排。野战军队的部队经常驻扎在市井居民区，而边防军的部队则有固定基地。

大多数边防军都驻留在元首制时期的军团和辅助单位所驻扎的​​基地一些编制较大的边防军单位(军团和布旗队)驻扎于城市,可能会有永久性的营房。 由于边防军在同一个地区活动,有自己的营地,而且往往从同一地区招募,因此他们往往与当地人保持较好的关系,这与经常被调往其他地区的野战军和中央军不同, 他们经常被安置在平民家中。

野战的部队,包括中央军,野战军,有时甚至是伪野战军,通常宿于非战区的城市内,在战时则宿于临时营地。但通常不会像边防军那样在单个城市内的永久基地长期驻扎。从法律证据上看，他们通常被强制性地安置在私人住宅中 (hospitalitas). 这是因为他们经常在不同的省份过冬。常备扈从军陪着皇帝四处征战, 而地区的扈从军 则根据作战需求改变驻扎地。然而在五世纪时期皇帝鲜少直接参与战事，因此在冬季常备常备扈从军的冬季基地变得更加固定。 西部的常备扈从军通常驻扎在Mediolanum (米兰)而东部的两支常备扈从军驻扎在君士坦丁堡附近。

军团的变革

四世纪时期对于军队建制最大的改变就是减少了单一单位的规模而增加了单位的数量，比起过去的军团/辅助军的二元制度而言增加了新的建制类型和等级使得这一系统更为复杂。

军事单位的建制规模

395年东罗马帝国的中央第二常备军大元帅麾下军团的盾徽。摘自反映罗马军队指挥架构的百官志的中世纪晚期抄本

古典晚期的帝国军队单位兵力的相关史料非常零散，而且模棱两可 下表按单位类型和等级给出了一些单位兵力估计:

四世纪罗马陆军单位建制规模

骑兵 单位	野战军 (包括中央军)	边防军	XXXXX	步兵 单位	野战军 (包括中央军)	边防军
边防骑兵大队		120–500		辅助步兵团	400–1,200
边防骑兵连		200–300		边防步兵大队		160–500
边防骑兵队		80–300		军团	800–1,200	500–1,000
教导团*	500			边防步兵队		200–300
布旗队**	400–600			边防民兵团		200–300

*教导团 不适用于 野战军编制，他是御林军的编制

** 布旗队有时也被叫做"骑兵队",比如说斯塔布勒希亚尼骑兵队

很多不确定因素仍然存在，特别是关于边防军军团的编制,其基础编制规模的估算上下差非常大.在4世纪的过程中,单位兵力也有可能发生变化。例如，瓦伦提尼安一世似乎与他的兄弟和共治皇帝瓦伦斯一起拆分了大约150个扈从军单位。由此产生的部队可能只有母部队的一半兵力(除非举行了一次大规模的征兵活动，使他们全部达到原来的兵力)。

教导团根据六世纪的参考资料，其编制在500人左右。

在扈从军中,人们一致认为布旗队的规模在500人左右，而军团则为1000人. 最大的不确定因素是最初由君士坦丁组建的辅助宫廷卫军编制。相关史料是矛盾的，表明这些部队可能是约500人，也可能是约1000人，或者介于两者之间。 如果较高的1000人的规模是真的，那么辅助步兵团和军团就别无二致，这是支持辅助步兵团为500人最有力的论据。

边防军的单位建制众说纷纭。Jones和Elton根据少量而模棱两可的史料认为，边境的军团的编制在1000人上下而同地区的其他单位只有500员的编制。 另一些人则根据纸莎草纸和最近的考古证据，认为边防军的平均兵力可能是Jones/Elton所声称的一半，即军团只有500人而其他的单位甚至只有250人的编制。

不同等级的作战单位

御林军

尽管从4世纪初该单位便已存在,但现有的唯一一份完整的御林军的清单则记载在成书于四世纪晚期到五世纪初期百官志中。。那时候一共有12支教导团,西帝国有5支分队而剩下7支在东帝国。这些护卫骑兵总计有6000人,相比于2世纪后期只有2000人的奥古斯都独属骑兵队equites singulares Augusti，编制增加为原来的三倍。 12支教导团中有10支是所谓罗马的"传统"骑兵,和元首制时期的大队骑兵的装备类似,下辖则有名为scutarii ("盾骑兵"), armaturae ("装甲骑兵") or gentiles ("异族骑兵")。然这些名字早已没有字面上的含义，已经成为了单纯的一种尊称,尽管他们最初可能表示由特殊的装备或种族组成的部队(gentiles意为被吸纳入境内服兵役的异族的部落民)。只有东部的两支教导团,是极为特殊的建制: 一支教导团名为clibanarii (具装冲击骑兵,或者是重具装冲击骑兵),还有一支则是具装弓骑兵(sagittarii). 40 select troops from the scholae,而从御林军中被选出的40名因其白色制服而被命名的candidati,是皇帝的私人保镖

中央军和野战军

参见：Palatini (Roman military)、Comitatenses和Pseudocomitatenses

中央军和野战军的基础骑兵分队被称作中央军布旗队和野战军布旗队;同样基础的步兵分队被称作中央军军团, 中央军辅助步兵团, 野战军军团和伪野战步兵团. 只有中央军会有辅助步兵团, 以强调其精英地位, 而军团在中央军和野战军都有。

扈从军的骑兵的大多数(61%)一直保持着半具装的类型,与元首制时期的骑兵大队类似，通常在战场上被用于近战。 这些军团具有各种头衔: 野战骑兵团comites,盾骑兵团equites scutarii,侍卫骑兵团或万用骑兵团equites promoti。同样，这些头衔可能纯粹仅是遵照旧日传统，并不表示不同的部队类型或职能。 24%的骑兵军团是无装甲轻骑兵,例如达尔马提亚骑兵队, 毛里人骑兵队 or 弓骑兵部队,他们适合骚扰和追击敌军。 毛里人自500年前的第二次布匿战争以来一直存在于帝国的辅助骑兵的行列。 达尔马提亚骑兵,则是自三世纪开始出现在罗马军队内。 扈从军的15%的骑兵部队则是重装甲的甲胄冲击骑兵 or 具装冲击骑兵, 用于冲击敌军阵列

至于步兵和元首制时期并未有什么不同，与2世纪的辅助兵团的装备别无二致，唯有轻微的调整 (请参看下面的Equipment).

边防军

主条目：边防军

边防军里, 什么上述的单位编制几乎都有，步兵包括了边防步兵队, 边防民兵团以及辅助步兵团,或者还有些元首制时期遗留下来的军团和大队建制。骑兵建制的话则包含了边防骑兵队, 边防骑兵连和 元首制时期遗留下来的骑兵大队.

野战军的实力要强于边防军的证据多且充分,但是差距并非天差地别。有说法指出边防军的组成大多来源于地方农民的民兵,因此作战能力远不是职业军人的对手。这种观点被许多现代学者所否定。史料中证明边防军实际上都是全职的职业军人。 他们负责打击小规模劫掠的蛮族,这是帝国持久的安全问题。因此，他们的战斗准备和经验很可能是很高的。这一点在阿米达围城战（359年）中表现得淋漓尽致，被围困的边防军团以高超的技巧和顽强的意志抵抗了波斯人的进攻。虽然波斯人的规模优势要远高于守城的罗马守军和援军（12万人对5万）,波斯人取得了胜利并绞死了当时的守城指挥官,但是波斯人也付出了超过3万人的重大损失,而罗马方面仅牺牲了绝大多数的守军和城外的流民,援军并未遭到重创。 埃尔顿认为，资料中没有提到少于400人的野蛮人入侵，这意味着这种情况通常由边防军处理，而不需要扈从军的协助。'. 边防军同时也经常陪同扈从军以作为特定战役的辅军,之后也会长期跟随扈从军并被称为伪野战军,对其战斗力的认可不言而喻。

特殊建制

伊朗克尔曼沙汗省“花园拱门”的萨珊王朝的重甲骑兵浮雕。他身穿的可能是带护脸的锁子甲。 这可能是罗马人所说的clibanarius盔甲, 暗示穿着如此全具甲的人在甲内如同呆在烤炉内一般热。此处要注意的是,骑兵的马匹也是有盔甲的。

外部圖片链接
Roman cataphract cavalryman

罗马晚期的军队中有大量的重装甲骑兵，被称为cataphractarii (来自于希腊语κατάφρακτος/kataphraktos，意思是全身被包覆着的).骑兵从脖子到脚包覆着层状的鳞甲 或者躯干四肢穿着札甲(可以参照臂甲),他们的马匹通常也包覆着盔甲。 具甲骑兵持有名为contus的重型长枪,长约3.65米（12英尺）,需要双手抓持，部分人还佩带弓箭。 具甲骑兵主要负责冲击敌阵,通过集中压倒性的兵力攻击敌方阵线的某一特定地段来打破敌方阵线。在4世纪的记录中，还出现了一种被称为 具装冲击骑兵的冲击骑兵,这个词源于希腊语的κλίβανοςklibanos (即面包的烘焙炉)当然也有说法是起源于波斯语. 也许就是甲胄冲击骑兵的代称，也或者是这其中的一种。 这种骑兵的原型公元前六世纪便存在在欧亚大草原斯基泰人和他们的同族[[萨尔马提亚人|萨尔马提亚人|]的部落中。公元前1世纪,安息帝国便采用了这种军种。再至公元一世纪时期，为了对抗东方波斯人和北方多瑙河流域的游牧萨尔马提亚人的威胁，铁甲骑兵成为罗马人的军队的一部分。 通过考古发掘最早的铁甲骑兵部队来自于2世纪时开始存在的高卢-潘诺尼亚甲胄骑兵大队，当时驻扎在潘诺尼亚,即现在的匈牙利 罗马帝国境内的甲胄骑兵存在已久，但再帝国的后期规模才开始大规模增加，帝国大多数的甲胄骑兵军团就驻扎在东部地区。 不过，在驻扎在东部军队的兵团中,有几个兵团的名称是高卢语,很显然起名的根源起于帝国的西部。

弓箭手部队在百官志中以equites sagittarii (弓骑兵)以及sagittarii (弓箭手,词源sagitta意为"羽箭").与元首制时期类似,许多非sagittarii命名的军团也可能包含一些弓箭手。弓骑兵似乎只出现在轻骑兵部队中。 弓箭手和弓骑兵同时都被存在于扈从军中。 而边防军只会有弓骑兵的编制,因为步兵里面已经混入了步兵弓箭手。

古典晚期的帝国军队的一个显著特点是出现了独立的炮兵部队,在元首制时期这些部队似乎是军团的组成部分。他们一般被称之为弩炮部队ballistarii (来源于Ballista即投射器的意思), 百官志内一共有七个基础单位编制，不过只有一个归属于中央军编制下。但也有一些被标明为'伪野战军,意味着它们原本属于边防部队。独立炮兵部队的目的大概是为了大量集中火力,尤其是对围攻有用。然而，许多普通的军团很可能继续拥有integral artillery, 尤其是边防部队。

百官志当初还列出了一系列疑似特殊功能的轻步兵单位: superventores和praeventores (阻击队) exculcatores (追踪队), exploratores (斥候队).但是同时期记叙此事的阿米安努斯用了多种不同术语来描述这些部队: velites'(轻装远程投掷队), leves armaturae(投石者部队), exculcatores(追踪队), expediti(探查队). 即使百官志内证实阿米安努斯所说的这些部队是独立部队单位,目前为止尚不清楚这些部队中是否有任何一支是独立的部队,或者实际上只是为某一特定行动而专门武装的普通部队的小分队。

部曲

主条目：Bucellarius

布塞拉里亚Bucellarii (拉丁文复数为bucellarius;字面意义是"食饼干者", 希臘語：βουκελλάριοι)是晚期Roman 和[東羅馬帝國|Byzantine Empire]]时期出现的职业士兵的称呼,这些部队不由国家直接支持,通常都由个人所雇佣并效忠于其雇主,不过他们也宣誓服从在位皇帝。这些 "家丁部队 "的雇主通常是著名的将军或高级文官僚。这些部队的单位一般都很小，但是，特别是在许多内战期间，他们可以发展到几千人。实际上, 因为部曲是受雇佣的小规模的个人部队，所以他们的装备通常要好很多，训练也相当充分，战斗力要优于正规军。他们最早出现于四世纪后期，随着时间的流逝他们逐渐成为战斗部队中的中流砥柱，尤其是远征军。著名的部曲雇主包括了作为军方大元帅的 斯提里科 和埃提乌斯,还有大区司政官鲁菲努斯.

蛮盟佣兵

在正规军之外帝国雇佣了大量的从罗马帝国境外的部队,通常被称为蛮盟 (该词源于foedus 即"条约"之意)佣兵,或者在东方他们被称为symmachi。T这些部队的人员通常都来自于蛮族酋长们的土地，他们的部落领主与帝国签订条约dediticii而为帝国四处征战。 罗马人在整个帝国史上都在使用这些部队,比如说图拉真柱所刻画的战争场景上,蛮盟佣兵在达契亚战争中立下了汗马功劳。 (101–6).

在四世纪元首制式微之后，随着越来越多的蛮族进入罗马帝国正规部队，蛮盟佣兵的编制和所属越来越难以界定，他们根据他们所属的族群被编在一起，成为被称为”Numeri”的部队。(该词即部队之意, 虽然numerus也是正规步兵建制的名称).他们在特定战役期间或特定时期与正规军一起服役。通常他们的服役范围仅限于部落所居住的地区，但有时也可以部署到其他地方。 他们由自己的领袖指挥。目前还不清楚他们使用的是自己的武器和盔甲还是罗马军队的标准装备。在晚期军队中，比较有战斗力的和在军中长期服役的numeri似乎被吸收到晚期的正规军中，迅速变得与其他部队没有区别。

兵员的征募

于罗马人

元首制时期，大多数的罗马军团和辅助军团的新兵都是志愿兵(voluntarii)。当然强制征兵(dilectus)并未被完全废除，但仅仅会在紧急情况或者中大作战需要大量补充兵员的情况才会用到。 与此形成明显对比的是，古典晚期的军队对罗马公民的招募主要依靠强制征兵。首先，法律规定现役军人或老兵的儿子必须入伍。其次，根据indictio（土地税评估）每年定期进行征收。土地所有者（或土地所有者的组织）要根据其庄园应缴纳的地税数额，向军队提供相应数量的新兵。自然，地主们有强烈的动机留住自己最优秀的年轻人在自己的庄园里工作，而把那些体质较差或不可靠的人送去服兵役。还有证据表明，他们试图通过提供士兵（无论如何都有可能服役）和流浪汉（vagi）的儿子来完成他们的配额来欺骗征兵。

然而，征兵制实际上并不普遍。首先，以土地为基础的征兵意味着征兵对象完全是农民的儿子，而不是城镇居民。 因此，帝国约有20%的人口被排除在外。 在元首制时期类似，奴隶是不可征召的，自由民里的某些职业从业者例如面包师和旅馆老板也不在征兵之列。此外，省级官员和curiales(市议会议员)也不能被征兵。这些规定只有在紧急情况下才会放宽，如在405-406年的军事危机期间(拉达盖苏斯' 率领大量蛮族入侵高卢和北意大利)。最重要的是，征兵要求往往折算成现金征收，按每一个应征者的固定比率征收。这在某些省份、某些年份是这样做的，不过具体细节基本不详。从现有的极少证据来看,征兵并非在各省均匀实施,而是主要集中在军队的传统征兵地区,类似高卢 (莱茵河沿岸的两个日耳曼日亚行省)和多瑙河沿岸省(例如潘诺尼亚,默西亚和色雷斯), 其他地区大概也经常折算。对350-476年间已知的野战军兵员的来源进行分析，在帝国西部政府的军队中，伊利利里亚和高卢管区共提供了52%的新兵。尽管全帝国12个管区里多瑙河的沿岸管区只有3个，但这三个管区提供了全军接近一半的兵员，这与元首制时期极为相似。 This picture is much in line with the 2nd-century position.

准新兵必须接受身体检查。新兵必须年龄在20-25岁之间，这个范围在4世纪后期延伸到19-35岁。新兵必须要身体健康，必须要满6 罗马尺 (5 ft 10in, 178 cm)而到了367年,这个标准到367年被降低至5尺3 寸s (5 ft 7in, 170 cm). 维盖提乌斯暗示，在帝国很晚期（约公元400年），甚至这一身高要求可能已经放宽，因为"... 如果有需求的话，与其说考虑身材，不如考虑力量。即使荷马本人也不需要见证者，因为他记载堤丢斯泰德乌斯身材矮小，但却是一个强壮的战士"。

一旦新兵被录取，他就会在手臂上打上 "标记"，多半是纹身或烙印，以便在他试图开小差时被识别出来。 然后，新兵会被发放一个身份识别盘(戴在脖子上)和一份入伍证书(probatoria)。然后，他会被分配到一个军团.375年的一项法律规定，身体素质较好的人必须被分配到野战军中. 在4世纪,最低服役年限为20年(边防军则是24年). 相比之下，在元首制时期，罗马军团和辅助兵团士兵的服役年限均为25年。

广泛采用征兵制、强制征召士兵的儿子、放宽年龄和身高要求以及给新兵打上烙印，所有这些都表明，军队在寻找和留住足够的新兵方面存在严重困难。 Recruitment difficulties are confirmed in 征兵困难在法典证据中得到了证实：对于为逃避兵役而自残的情况（如砍掉大拇指），有一些处理措施，包括386年的一项极端法令，要求将这些人活活烧死。 逃兵显然是一个严重的问题，而且可能比元首制时期严重得多，因为后者主要是志愿役。这一点可以从准予休假 (commeatus)的规定变得更为严格得到佐证。在2世纪，士兵的休假由其团长酌情批准，而在4世纪，休假只能由高级军官(督军,野战军司令,大元帅)进行批准。 此外，扈从军部队似乎在一般状态下都会缺员三分之一。 官方与实际兵力之间的巨大差距是招募问题的有力证据。对此，Elton认为，后期军队并不存在严重的征兵问题，其依据是大量人免于征兵。

于蛮族

(追溯至约390年的)出现在Constantinople的狄奧多西方尖碑基座浮雕后排的古典晚期罗马军队,他们可能出身与蛮族。这些军队归属于中央军,负责保护皇帝。当时中央军中超过三分之一的士兵是出身于蛮族的。请注意带有军团吊坠的项链和长发，这是蛮族新兵带来的风格，与元首制时期保持短发的传统截然不同。

Barbari ("蛮族")通常被罗马人用来形容帝国境外的住民,这个词来源于希腊语，用以指代喋喋不休说着难以理解语言的外人。

大多数学者认为，在整个元首制时期，绝大多数的蛮族 barbari'都招入了辅助军团 (因为罗马军团仅招募罗马公民). 然而，在3世纪之前几乎没有史料证明这一点。当然也有稀少的证据表明，如果不是全部，辅助军团的绝大多数兵员也是来自于 罗马的自由民 或者罗马公民。 4世纪的军队可能比两三百年前的元首制部队更依赖于对蛮族的招募，而其中的依据如下:

1. 《百官志》内列出了帝国境内的一些蛮族军事定居点，他们被称为军户或者异邦人gentiles,这些蛮族定居者都是军队招募新兵的重点对象。 日耳曼或萨尔马提亚部落的人获得帝国赐予的土地，作为交换他们将为帝国服兵役。有可能每个部落都有条约义务，每年向军队提供一定数量的兵员 蛮族部落居民在帝国内重新定居以换取兵役，在4世纪并不是一个新的现象:它可以追溯到奥古斯都时代。 只不过四世纪开始这种现象的规模开始扩展，而做法开始系统化。
2. 百官志内的单位有许多拥有蛮族的命名，因为他们是跟着本族长官一起作为非正规军的蛮盟佣兵(被称为socii或foederati) 转正成为了帝国的常备军的结果。在元首制时期，带有蛮族名字的正规军单位名字直到3世纪开始才有记载,但仍然极少。比如说第一萨尔马提亚骑兵大队ala I Sarmatarum便在3世纪英格兰被证实在那驻扎,无疑是175年派驻在那里的萨尔马提亚骑兵的后羿。
3. 正规军中出现了相当数量的带有蛮族姓名的高级军官，并最终出现在军方顶层. 5世纪初期，西帝国的军队常由蛮族出身或者蛮族血统的将军所把持,比如阿波加斯特,斯提里科以及李希梅尔.
4. 4世纪的军队采用蛮族(尤其是日耳曼人)的服饰、习俗和文化，意味着蛮族的影响增强。比如说罗马军队的一部分单位采用仿蛮族的命名，如角盔Cornuti,指的是德国人在头盔上用角做装饰的习俗, 还有 barritus,是日耳曼人的战吼。在中央军军团内，因为蛮族兵员愈发见多，日耳曼人传统的留长发习惯成为了一种风俗。

对4世纪军队中出身于蛮族的兵员比例的量化是高度推测出来的结果。Elton基于少量的史料基础上进行了最详细的分析。根据这一分析，在350-400年期间，样本部队中大约四分之一的军官出身于蛮族。以每十年进行的分析表明，这一比例在这一时期没有增加，实际上在5世纪初也没有增加。后一种趋势意味着基层军官中蛮族的比例并没有增加多少，否则蛮族军官的比例会随着时间的推移而增加，以反映这一点

如果蛮族在军中的比例在四分之一上下, 那么这个比例也比二世纪时期的正规军要高。假设将这个比例的兵员全部编入辅助军团的话,在辅助兵团占元首制军队的比例60%的情况下，那么超过40%的新兵将会是蛮族出身的。 不曾有过史料表明2世纪对蛮族如此之大的招募. 非罗马名字的士兵里面，75%是日耳曼人: 在百官志的建制中证实了这些人来自于法兰克人, 阿勒曼人, 萨克逊人, 哥特人,以及汪达尔人 。 其他重要的新兵来源是来自多瑙河地区的萨尔马提亚人;亚美尼亚人 以及出身高加索地区的伊比利亚人.

与罗马新兵相反，绝大多数蛮族新兵可能是自愿入伍的，他们被服役条件和职业前景所吸引，与他们在家乡的生活条件相比，这些条件和前景可能显得很理想。只有少数的蛮族军人作为过去的dediticii (向罗马帝国投降的降兵，或者是逃避与其他部落冲突而投靠帝国的军人)而被强行征召的,作为和平条件，他们不得不承诺每年提供一定数量的新兵。蛮族可以直接招募，作为个体加入正规军，也可以被间接招募，作为非正规的附属部队的成员转为正规军。

军阶，薪酬以及福利

普通士兵

在军衔金字塔的底部是普通士兵: pedes (步兵) and eques (骑兵).与2世纪的同行不同，4世纪士兵的食物和装备并不从他的军饷(stipendium)中扣除,而是免费提供的。 这是因为支付给士兵的军饷的第纳里乌斯银币,在戴克里先时期的价值远低于2世纪。在君士坦丁时期，它失去了剩余价值，在4世纪中叶停止定期支付。

士兵唯一的可支配收入来自捐献金donativa, 即皇帝定期发放的现金红利，因为这些红利是以从未贬值的金币solidi或者纯银的方式进行发放。奥古斯都在位期间，每5年定期发放5枚苏勒德斯 。同时当奥古斯都即位之时，士兵们会被一次性再发放5枚苏勒德斯以及一磅纯银 (一磅纯银可以换算成4枚苏勒德斯，根据推算士兵一次性可以获得等同9枚苏勒德斯当量的奖金。帝国西部从284年到395年经历了12位奥古斯都，每个平均任期都有9年，这些士兵的捐献金平均下来为每年1枚苏勒德斯金币。故士兵的可支配收入平均每年至少有2个苏勒德斯。当然同时期也可能不仅会有来自新即位的奥古斯都的奖金，还会有来自新继位的凯撒的奖金。 而2枚苏勒德斯的年收入相比于元首制的二世纪时期而言，只有可怜的四分之一 (二世纪时期的士兵年收入换算成苏勒德斯大约在8枚左右). 同时帝国后期士兵们退役后的各类补偿（其中包括土地补偿）也远逊于过去，仅为元首制时期的十分之一。

尽管与元首制时期有差距,Jones和Elton认为与大多数新兵的农民家庭不得不忍受的温饱水平的艰难现实相比，4世纪的薪酬还是很有吸引力的。与此相对应的是，兵役显然不受欢迎。

然而，在等级更高的部队中，薪酬会更有吸引力。薪酬金字塔的顶端是御林军 的士兵们。再接着是中央军Palatini，然而是野战军Comitatenses，而边防军Limitanei则位居最后。关于各等级之间的薪资差异的史料很少，但它们是相当大的，这可以从一个例子中看出:一个扈从军军团的书记官 (军中的军需官)就比准野战军的军需官的工资高了50%。

军团级军官

旧建制军团级军官(罗马军团, 骑兵大队和步兵大队)在元首制时期保持不变，其中包括了百夫长和十夫长。然而在改革后的新建制中，(例如布旗队, 辅助步兵团之类), 已有史料证实出现了多个不同的军阶,似乎是仿照地方当局官僚的头衔而设立的。 众人对这些军衔知之甚少，以至于无法确定地将其与传统军衔等同起来。维盖提乌斯声称两百夫长ducenarius, 顾名思义，指挥200人。如果是这样的话，4世纪的百夫长可能仍相当于旧式部队中的百夫长。 如下是当前最准确的薪金等级表:

四世纪的军团级军官

薪金等级 (多少倍于基层士兵的收入)	2世纪的大队（升序）	四世纪的同类型建制)
1	步兵 (pedes)	步兵 (pedes)
1.5	口令官 (tesserarius)	士官长 (semissalis)
2	百人队布旗手 (signifer) 副百夫长 (optio) 步兵大队布旗手 (vexillarius)	十夫长 (骑兵的为circitor) (步兵的为biarchus)
2.5 to 5		百夫长 centenarius (2.5) 两百夫长 ducenarius (3.5) 军团参谋 senator (4) 副军团长 (5)
Over 5	百夫长 centurio 首席百夫长 centurio princeps 副大队长 beneficiarius

注: 军阶仅针对于薪金的高低，与在军队中的职能并不完全相关

该表显示，4世纪兵团高级军官得到的的薪资差额远小于2世纪的同行，在4世纪高级的行政系统官员也出现了同样的现象。

军团及军队级指挥官

四世纪军团及军队级指挥官薪金表

薪金等级 (多少倍于基层士兵的收入)	等级 (升序)	官位数目 (Notitia)	职责描述
12	预备役军官 Protector	数百人 (尤利安时期为200人左右)	预备役军团长官
未知	军事保民官 Tribunus (也可以称praefectus)	c. 800	军团长官
未知	侍卫保民官 Tribunus comes	数量未知	(i) 皇帝贴身侍卫长官 (ii) 两个军团的长官 (iii) 御林军下分支指导团长官(类比Domesticus) (iv) 皇帝或军方高层下的副官
100	边防督军 Dux(极少的会被称为comes)	27	边区军队的总长官
未知	野战军司令 Comes rei militaris	7	(i) 管区的小型扈从军总长官
未知	大元帅 Magister militum (西部称为骑兵元帅magister equitum)	4	各管区的大型扈从军总长官
未知	常备军大元帅 Magister militum praesentalis (西部称为骑兵元帅magister utriusque militiae)	3	中央常备军总长官

上表显示了持有委任状(sacra epistula, 字面意庄严之信)的军阶，而委任状会由皇帝在专门的仪式上亲自颁发给被委任者。

在西西里岛皮亚扎阿尔梅里纳的一副表现了狩猎场景的四世纪马赛克壁画。画中出现的可能是穿着非战斗制服的罗马军官 (没有穿着盔甲与头盔，但是持有盾牌与长矛) 。而贯穿整个帝国时代，士兵都是以非战斗形象出现的。 注意灰白色的丘尼卡。左边外衣上绣的卍字符号,可能源于印欧人的传统, 代表宇宙，罗马人常将其作为装饰图案。同时也要注意他们披着的斗篷(chlamys)和穿着的裤子。他们盾牌上的图案表示持盾者的军团。同时也请注意袖子和肩膀上刺绣的带子。

预备役军团长官(预备役军官protectores)

4世纪的一项重大创新是预备役军团，其中包括预备役军团的高级军官。按理预备役军团长本应是历经百战的老兵所担任, 但从军队外招收军方相关年轻人(往往是高级军官家族子弟)已成为一种普遍做法。预备役军官组成的团体既可以培训军官，也可以提供为大元帅或皇帝执行特殊任务的参谋人才。隶属于皇帝的预备役军官被称作宫内侍卫官,分成四个指导团并由侍卫保民官指挥。军中效力数年之后, 他们会被皇帝授予委任状, 并被安排指挥一个军团。

军团长官(军事保民官tribuni)

军团指挥官可以被称为三种头衔中的任意一个: tribunus (对应扈从军军团或者边区的大队), praefectus (通常是边防军的军团)或者praepositus (指挥边防步兵队和蛮盟佣兵). 然而tribunus被通俗地用来表示任何军团的指挥官。虽然大多数tribuni 是从预备役军官团体中进行任命, 但也有少数人，同样主要是以高级现役军官的子弟为主，他们直接空降到军团内成为麾下士兵的长官。 军团指挥官的地位因其部队的等级不同而有很大的差别。在最高端，御林军的指挥官会被授予伙友comes的荣衔, ，这种做法在公元400年后成为标准流程。

高阶军团长官(侍卫保民官tribuni comites)

comitiva,亦称御用伙友,是君士坦丁一世为表彰高级行政和军事官员,特别是皇帝的随从设立的荣衔。它与已有的元老院和骑士的荣衔有部分重叠,因为它可以授予前两者集团其中之一的成员(当然也可以授予这两者之外的外人)。 伙友可以分为三级, 由于过度授予,只有第一等级的伙友, comes primi ordinis (直译为第一等级的伙友,只授予元老院成员), 在450年以后还保留着价值。在许多情况下，这个头衔是依职权授予的，可以说是纯粹的荣誉性头衔。

在军方,comes primi ordinis的头衔会授予那些资深军事保民官。比如说(1) 宫内侍卫官的头领侍卫保民官,这个头衔在350年的时候被称为comes domesticorum; (2) 御林军的保民官: 在公元400年后御林军指挥官也常被授予这个头衔 (3) 同时指挥两个扈从军军团的长官 (指常常成对出动的军团,例如朱庇特军团和赫拉克勒军团); (4) 一些为皇帝和元帅效劳但没有军团指挥权的护民官 (tribuni vacantes), .但是，以上这些官员在等级上终究和指挥管区小型扈从军的野战军司令不同，后者可以指挥管区的小规模的扈从军，而不仅仅是一到两个军团。

军方高层(督军,野战军司令,大元帅)

由数个军团组成的大兵团的指挥官，依照实力大小，称为:边区督军,野战军司令和大元帅.这些军官的军衔相当于现代军队中的将军和元帅。

边区督军(少数会称为司令),负责指挥边境省份的军队以及边区河道内的船队。直到君士坦丁一世时期, 边区督军向所属管区的代理官汇报工作。360年之后,督军则对当地驻扎的扈从军指挥官，例如大元帅或野战军司令负责。 不过，他们有权直接向皇帝报告,这个可以从皇帝敕令中可以看得出来。少量的边防军长官也被称为司令,比如驻扎在不列颠沿海的comes litoris Saxonici (萨克森海岸边防军司令")。

野战军司令一般指挥一个较小规模的管区扈从军(规模通常在10000人左右)。在百官志成书时期,野战军司令通常出现在帝国西部,因为西部的扈从军被分割成数个小型野战军。而在东部就只有两位野战军司令, 负责指挥埃及和伊苏利亚的军队,但这些人只指挥边防军的军团。这是因为他们在百官志成书时期,直接向皇帝本人汇报工作(当然之后他们则对东方野战军元帅负责了)。 管区的野战军司令还负责指挥管区内的边防督军。

大元帅统领着大规模的管区扈从军(规模通常在20000-30000兵员之间)。与西部的野战军司令一样，东部的大元帅们也能够指挥其管区下所有的边防督军。

常备军大元帅是中央扈从军的总指挥(规模通常在20000-30000兵员之间)。和西部的两军大元帅,骑兵统帅和步兵统帅同等级。

从中基层升到兵团指挥官的比例已不得而知,不过多半可能性很小,因为大多数人在被授予一个军团的指挥权时已经接近退休年龄。相反的是,直接被皇帝委任的预备役军官和军事保民官把持了上升的渠道,因为他们常常是年轻人。对于这些人来说，晋升为军方高层的速度可以很快。例如狄奥多西，28岁便做了边区督军。 而且晋升也可以适当略过一些军阶,比如说御林军的长官享有直接接触皇帝机会, 比其他人更容易成为大元帅: 比如说出身蛮族的阿吉洛 在360年直接从御林军的军事保民官直接越过边区督军的阶段,直接晋升成为大元帅。

Equipment

Frieze (bottom) showing Constantine I's cavalry driving Maxentius' troops into the River Tiber at the Battle of the Milvian Bridge (312). The image proves that 4th-century soldiers wore metal body armour (the Maxentian soldiers are wearing either mail or scale, it is unclear which). The Constantinian cavalry is apparently unarmoured, probably because these were units of Illyrian light cavalry (equites Dalmatae) and mounted archers. Detail from the Arch of Constantine, Rome

Detail of bas-relief on base of former Column of Theodosius in Constantinople (Istanbul). Date c. 390. Roman soldiers in action. Note soldier at centre had an Intercisa-style helmet with iron crest (prob. indicating officer rank) and is wearing chain-mail or scale armour, evidence that Vegetius's claim that infantry dropped helmets and armour in the later 4th century is mistaken. Istanbul Archaeological Museum

Late Roman helmet, called the Deurne helmet. It is covered in expensive silver-gilt sheathing and is inscribed to a cavalryman of the equites stablesiani.

The basic equipment of a 4th-century foot soldier was essentially the same as in the 2nd century: metal armour cuirass, metal helmet, shield and sword. Some evolution took place during the 3rd century. Trends included the adoption of warmer clothing; the disappearance of distinctive legionary armour and weapons; the adoption by the infantry of equipment used by the cavalry in the earlier period; and the greater use of heavily armoured cavalry called cataphracts.

Clothing

In the 1st and 2nd centuries, a Roman soldier's clothes consisted of a single-piece, short-sleeved tunic the hem of which reached the knees and special hobnailed sandals (caligae). This attire, which left the arms and legs bare, had evolved in a Mediterranean climate and was not suitable for northern Europe in cold weather. In northern Europe, long-sleeved tunics, trousers (bracae), socks (worn inside the caligae) and laced boots were commonly worn in winter from the 1st century. During the 3rd century, these items of clothing became much more widespread, apparently common in Mediterranean provinces also. However, it is likely that in warmer weather, trousers were dispensed with and caligae worn instead of socks and boots. Late Roman clothing was often highly decorated, with woven or embroidered strips, clavi, circular roundels, orbiculi, or square panels, tabulae, added to tunics and cloaks. These colourful decorative elements usually consisted of geometrical patterns and stylised plant motifs, but could include human or animal figures. A distinctive part of a soldier's costume, though it seems to have also been worn by non-military bureaucrats, was a type of round, brimless hat known as the pannonian cap (pileus pannonicus).

Armour

Legionary soldiers of the 1st and 2nd centuries had use of the lorica segmentata, or laminated-strip cuirass, as well as mail (lorica hamata) and scale armour (lorica squamata). Testing of modern copies have demonstrated that segmentata was impenetrable to most direct and missile strikes. It was, however, uncomfortable: reenactors have discovered that chafing renders it painful to wear for longer than a few hours at a time, and it was also expensive to produce and difficult to maintain. In the 3rd century, the segmentata appears to have fallen out of use and troops were depicted wearing mail or scale.

In either the 390s or the 430s), Vegetius reports that soldiers no longer wore armour:

From the foundation of the city till the reign of the Emperor Gratian, the foot wore cuirasses and helmets. But negligence and sloth having by degrees introduced a total relaxation of discipline, the soldiers began to think their armor too heavy, as they seldom put it on. They first requested leave from the Emperor to lay aside the cuirass and afterwards the helmet. In consequence of this, our troops in their engagements with the Goths were often overwhelmed with their showers of arrows. Nor was the necessity of obliging the infantry to resume their cuirasses and helmets discovered, notwithstanding such repeated defeats, which brought on the destruction of so many great cities. Troops, defenseless and exposed to all the weapons of the enemy, are more disposed to fly than fight. What can be expected from a foot-archer without cuirass or helmet, who cannot hold at once his bow and shield; or from the ensigns whose bodies are naked, and who cannot at the same time carry a shield and the colors? The foot soldier finds the weight of a cuirass and even of a helmet intolerable. This is because he is so seldom exercised and rarely puts them on.

It is possible that Vegetius' statements about the abandonment of armour were a misinterpretation by him of sources mentioning Roman soldiers fighting without armour in more open formations during the Gothic wars of the 370s. Evidence that armour continued to be worn by Roman soldiers, including infantry, throughout the period is widespread.

The artistic record shows most late Roman soldiers wearing metal armour. For example, illustrations in the Notitia Dignitatum, compiled after the reign of Gratian, indicate that the army's fabricae (arms factories) were producing mail armour at the end of the 4th century. The Vatican Virgil manuscript, early 5th century, and the Column of Arcadius, reigned 395 to 408, both show armoured soldiers. Actual examples of quite large sections of mail have been recovered, at Trier (with a section of scale), Independența, and Weiler-la-Tour, within a late 4th-century context. Officers and some soldiers may have worn muscle cuirasses, together with decorative pteruges. In contrast to the earlier segmentata plate armour, which afforded no protection for the arms or below the hips, some pictorial and sculptural representations of Late Roman soldiers show mail or scale armours giving more extensive protection. These armours had full-length sleeves and were long enough to protect the thighs.

The catafractarii and clibanarii cavalry, from limited pictorial evidence and especially from the description of these troops by Ammianus, may have worn specialised forms of armour. In particular their limbs were protected by laminated defences, made up of curved and overlapping metal segments: "Laminarum circuli tenues apti corporis flexibus ambiebant per omnia membra diducti" (Thin circles of iron plates, fitted to the curves of their bodies, completely covered their limbs). Such laminated defences are attested by a fragment of manica found at Bowes Moor, dating to the late 4th century.

Helmets

In general, Roman cavalry helmets had enhanced protection, in the form of wider cheek-guards and deeper neck-guards, for the sides and back of the head than infantry helmets. Infantry were less vulnerable in those parts due to their tighter formation when fighting. During the 3rd century, infantry helmets tended to adopt the more protective features of Principate cavalry helmets. Cheek-guards could often be fastened together over the chin to protect the face, and covered the ears save for a slit to permit hearing e.g. the "Auxiliary E" type or its Niederbieber variant. Cavalry helmets became even more enclosed e.g. the "Heddernheim" type, which is close to the medieval great helm, but at the cost much reduced vision and hearing.

In the late 3rd century a complete break in Roman helmet design occurred. Previous Roman helmet types, based ultimately on Celtic designs, were replaced by new forms derived from helmets developed in the Sassanid Empire. The new helmet types were characterised by a skull constructed from multiple elements united by a medial ridge, and are referred to as "ridge helmets". They are divided into two sub-groups, the "Intercisa" and "Berkasovo" types. The "Intercisa" design had a two-piece skull, it left the face unobstructed and had ear-holes in the join between the small cheek-guards and bowl to allow good hearing. It was simpler and cheaper to manufacture, and therefore probably by far the most common type, but structurally weaker and therefore offered less effective protection. The "Berkasovo" type was a more sturdy and protective ridge helmet. This type of helmet usually has 4 to 6 skull elements (and the characteristic median ridge), a nasal (nose-guard), a deep brow piece riveted inside the skull elements and large cheekpieces. Unusually the helmet discovered at Burgh Castle, in England, is of the Berkasovo method of construction, but has cheekpieces with earholes. Face-guards of mail or in the form of metal 'anthropomorphic masks' with eye-holes were often added to the helmets of the heaviest forms of cavalry, especially catafractarii or clibanarii.

Despite the apparent cheapness of manufacture of their basic components, many surviving examples of Late Roman helmets, including the Intercisa type, show evidence of expensive decoration in the form of silver or silver-gilt sheathing. A possible explanation is that most of the surviving exemplars may have belonged to officers and that silver- or gold-plating denoted rank; and, in the case of mounted gemstones, high rank. Other academics, in contrast, consider that silver-sheathed helmets may have been widely worn by comitatenses soldiers, given as a form of pay or reward. Roman law indicates that all helmets of this construction were supposed to be sheathed in a specific amount of gold or silver.

Shields

The classic legionary scutum, a convex rectangular shield, also disappeared during the 3rd century. All troops except archers adopted large, wide, usually dished, ovoid (or sometimes round) shields. These shields were still called Scuta or Clipei, despite the difference in shape. Shields, from examples found at Dura Europos and Nydam, were of vertical plank construction, the planks glued, and mostly faced inside and out with painted leather. The edges of the shield were bound with stitched rawhide, which shrank as it dried improving structural cohesion.

Hand weapons

The gladius, a short (median length: 460 mm/18 inches) stabbing-sword that was designed for close-quarters fighting, and was standard for the infantry of the Principate (both legionary and auxiliary), also was phased out during the 3rd century. The infantry adopted the spatha, a longer (median length: 760 mm/30 in) sword that during the earlier centuries was used by the cavalry only. In addition, Vegetius mentions the use of a shorter-bladed sword termed a semispatha. At the same time, infantry acquired a thrusting-spear (hasta) which became the main close order combat weapon to replace the gladius. These trends imply a greater emphasis on fighting the enemy "at arm's length". In the 4th century, there is no archaeological or artistic evidence of the pugio (Roman military dagger), which is attested until the 3rd century. 4th-century graves have yielded short, single-edged knives in conjunction with military belt fittings.

Missiles

In addition to his thrusting-spear, a late foot soldier might carry a spiculum, a kind of pilum, similar to an angon. Alternatively, he may have been armed with short javelins (verruta or lanceae). Late Roman infantrymen often carried half a dozen lead-weighted throwing-darts called plumbatae (from plumbum = "lead"), with an effective range of c. 30米（98英尺）, well beyond that of a javelin. The darts were carried clipped to the back of the shield or in a quiver. The late foot soldier thus had greater missile capability than his predecessor from the Principate, who was often limited to just two pila. Late Roman archers continued to use the recurved composite bow as their principal weapon. This was a sophisticated, compact and powerful weapon, suitable for mounted and foot archers alike. A small number of archers may have been armed with crossbows (manuballistae).

Supply infrastructure

The products of the fabricae, from the Notitia dignitatum. The illustration includes: helmets, shields, mail coats, cuirasses and laminated limb defences, plus various weapons.

Full-scale reconstruction of a 4th-century Roman river patrol-boat (lusoria), probably under the command of the dux of Germania I province. It is based on the remains of one of five late Roman river boats discovered at Moguntiacum in the early 1980s. The boat above, denoted Mainz Type A, had a long (22 m) and narrow (2.8 m) shape for speed and rounded keel to allow access to shallows. It could carry 32 marines, who rowed the boat fully armed (32 oars, 16 on each side). Whilst on board, the soldiers would hang their shields on stands fixed to the gunwales so as to provide cover from missiles launched from the riverbanks. Museum für Antike Schifffahrt, Mainz, Germany

A critical advantage enjoyed by the late army over all its foreign enemies except the Persians was a highly sophisticated organisation to ensure that the army was properly equipped and supplied on campaign. Like their enemies, the late army could rely on foraging for supplies when campaigning on enemy soil. But this was obviously undesirable on Roman territory and impractical in winter, or in spring before the harvest. The empire's complex supply organisation enabled the army to campaign in all seasons and in areas where the enemy employed a "scorched earth" policy.

Supply organisation

The responsibility for supplying the army rested with the praefectus praetorio of the operational sector. He in turn controlled a hierarchy of civilian authorities (diocesan vicarii and provincial governors), whose agents collected, stored and delivered supplies to the troops directly or to predetermined fortified points. The quantities involved were enormous and would require lengthy and elaborate planning for major campaigns. A late legion of 1,000 men would require a minimum of 2.3 tonnes of grain-equivalent every day. An imperial escort army of 25,000 men would thus require around 5,000 tonnes of grain-equivalent for three months' campaigning (plus fodder for the horses and pack animals).

Supply transport

Such vast cargoes would be carried by boat as far as possible, by sea and/or river, and only the shortest possible distance overland. That is because transport on water was far more economical than on land (as it remains today, although the differential is smaller).

Land transport of military supplies on the cursus publicus (imperial transport service) was typically by wagons (angariae), with a maximum legal load of 1,500 lbs (680 kg), drawn by two pairs of oxen. The payload capacity of most Roman freighter-ships of the period was in the range of 10,000–20,000 modii (70–140 tonnes) although many of the grain freighters supplying Rome were much larger up 350 tonnes and a few giants which could load 1200 like the Isis which Lucian saw in Athens circa 180 A.D. Thus, a vessel of median capacity of 100 tonnes, with a 20-man crew, could carry the same load as c. 150 wagons (which required 150 drivers and 600 oxen, plus pay for the former and fodder for the animals). A merchant ship would also, with a favourable wind, typically travel three times faster than the typical 3 km/h（2 mph） achieved by the wagons and for as long as there was daylight, whereas oxen could only haul for at most 5 hours per day. Thus freighters could easily cover 100 km（62 mi） per day, compared to c. 15 km（9 mi） by the wagons. Against this must be set the fact that most freighters of this capacity were propelled by square sails only (and no oars). They could only progress if there was a following wind, and could spend many days in port waiting for one. (However, smaller coastal and fluvial freighters called actuariae combined oars with sail and had more flexibility). Maritime transport was also completely suspended for at least four months in the winter (as stormy weather made it too hazardous) and even during the rest of the year, shipwrecks were common. Nevertheless, the surviving shipping-rates show that it was cheaper to transport a cargo of grain by sea from Syria to Lusitania (i.e. the entire length of the Mediterranean – and a ways beyond – c. 5,000 km) than just 110 km（68 mi） overland.

On rivers, actuariae could operate year-round, except during periods when the rivers were ice-bound or of high water (after heavy rains or thaw), when the river-current was dangerously strong. It is likely that the establishment of the empire's frontier on the Rhine-Danube line was dictated by the logistical need for large rivers to accommodate supply ships more than by defensibility. These rivers were dotted with purpose-built military docks (portus exceptionales). The protection of supply convoys on the rivers was the responsibility of the fluvial flotillas (classes) under the command of the riverine duces. The Notitia gives no information about the Rhine flotillas (as the Rhine frontier had collapsed by the time the Western section was compiled), but mentions 4 classes Histricae (Danube flotillas) and 8 other classes in tributaries of the Danube. Each flotilla was commanded by a praefectus classis who reported to the local dux. It appears that each dux on the Danube disposed of at least one flotilla (one, the dux Pannoniae, controlled three).

Weapons manufacture

In the 4th century, the production of weapons and equipment was highly centralised (and presumably standardised) in a number of major state-run arms factories, or fabricae, documented in the Notitia. It is unknown when these were first established, but they certainly existed by the time of Diocletian. In the 2nd century, there is evidence of fabricae inside legionary bases and even in the much smaller auxiliary forts, staffed by the soldiers themselves. But there is no evidence, literary or archaeological, of fabricae outside military bases and staffed by civilians during the Principate (although their existence cannot be excluded, as no archaeological evidence has been found for the late fabricae either). Late fabricae were located in border provinces and dioceses. Some were general manufacturers producing both armour and weapons (fabrica scutaria et armorum) or just one of the two. Others were specialised in one or more of the following: fabrica spatharia (sword manufacture), lanciaria (spears), arcuaria (bows), sagittaria (arrows), loricaria (body armour), clibanaria (cataphract armour), and ballistaria (catapults).

Fortifications

The Walls of Theodosius II at Constantinople, built 408–413, to increase the area of land protected by the original Constantinian walls. Note the massive crenellated towers and surviving sections of wall. The walls actually consisted of a triple curtain, each one overlooking the other. They proved impregnable to even the largest armies until the introduction of explosive artillery in the later Middle Ages

An example of late Roman fortification. Note the protruding towers to allow enfilading fire. The original height of both walls and towers was clearly greater than today, and the crenellations are not the original ones, but crudely cut from the curtain wall itself in the medieval period. The church visible inside the walls was built in the 12th century by the Normans. Portchester Castle, England. 3rd century

Relief with the liberation of a besieged city; Western Roman Empire, early 5th century, Museum of Byzantine Art (inv. 4782), Bode Museum, Berlin. Both cavalry and infantry are shown wearing body armour.

Compared to the 1st and 2nd centuries, the 3rd and 4th centuries saw much greater fortification activity, with many new forts built. Later Roman fortifications, both new and upgraded old ones, contained much stronger defensive features than their earlier counterparts. In addition, the late 3rd/4th centuries saw the fortification of many towns and cities including the City of Rome itself and its eastern sister, Constantinople.

According to Luttwak, Roman forts of the 1st/2nd centuries, whether castra legionaria (inaccurately translated as legionary "fortresses") or auxiliary forts, were clearly residential bases that were not designed to withstand assault. The typical rectangular "playing-card" shape, the long, thin and low walls and shallow ditch and the unfortified gates were not defensible features and their purpose was delimitation and keeping out individual intruders. This view is too extreme, as all the evidence suggests that such forts, even the more rudimentary earlier type based on the design of marching-camps (ditch, earth rampart and wooden palisade), afforded a significant level of protection. The latter is exemplified by the siege of the legionary camp at Castra Vetera (Xanten) during the revolt of the Batavi in 69–70 AD. 5,000 legionaries succeeded in holding out for several months against vastly superior numbers of rebel Batavi and their allies under the renegade auxiliary officer Civilis, despite the latter disposing of c. 8,000 Roman-trained and equipped auxiliary troops and deploying Roman-style siege engines. (The Romans were eventually forced to surrender the fort by starvation).

Nevertheless, later forts were undoubtedly built to much higher defensive specifications than their 2nd-century predecessors, including the following features:

1. Deeper (average: 3 m) and much wider (av. 10 m) perimeter ditches (fossae). These would have flat floors rather than the traditional V-shape. Such ditches would make it difficult to bring siege equipment (ladders, rams, and other engines) to the walls. It would also concentrate attackers in an enclosed area where they would be exposed to missile fire from the walls.
2. Higher (av. 9 m) and thicker (av. 3 m) walls. Walls were made of stone or stone facing with rubble core. The greater thickness would protect the wall from enemy mining. The height of the walls would force attackers to use scaling-ladders. The parapet of the rampart would have crenellations to provide protection from missiles for defenders.
3. Higher (av. 17.5 m) and projecting corner and interval towers. These would enable enfilading fire on attackers. Towers were normally round or half-round, and only rarely square as the latter were less defensible. Towers would be normally be spaced at 30米（98英尺） intervals on circuit walls.
4. Gate towers, one on each side of the gate and projecting out from the gate to allow defenders to shoot into the area in front of the entrance. The gates themselves were normally wooden with metal covering plates to prevent destruction by fire. Some gates had portcullises. Postern gates were built into towers or near them to allow sorties.

More numerous than new-build forts were old forts upgraded to higher defensive specifications. Thus the two parallel ditches common around earlier forts could be joined by excavating the ground between them. Projecting towers were added. Gates were either rebuilt with projecting towers or sealed off by constructing a large rectangular bastion. The walls were strengthened by doubling the old thickness. Upgraded forts were generally much larger than new-build. New forts were rarely over one hectare in size and were normally placed to fill gaps between old forts and towns. However, not all of the old forts that continued to be used in the 4th century were upgraded e.g. the forts on Hadrian's Wall and some other forts in Britannia were not significantly modified.

The main features of late Roman fortification clearly presage those of medieval castles. But the defensibility of late Roman forts must not be exaggerated. Late Roman forts were not always located on defensible sites, such as hilltops and they were not designed as independent logistic facilities where the garrison could survive for years on internal supplies (water in cisterns or from wells and stored food). They remained bases for troops that would sally out and engage the enemy in the field.

Nevertheless, the benefits of more defensible forts are evident: they could act as temporary refuges for overwhelmed local troops during barbarian incursions, while they waited for reinforcements. The forts were difficult for the barbarians to take by assault, as they generally lacked the necessary equipment. The forts could store sufficient supplies to enable the defenders to hold out for a few weeks, and to supply relieving troops. They could also act as bases from which defenders could make sorties against isolated groups of barbarians and to cooperate with relieving forces.

The question arises as to why the 4th-century army needed forts with enhanced defensive features whereas the 2nd-century army apparently did not. Luttwak argues that defensible forts were an integral feature of a 4th-century defence-in-depth "grand strategy", while in the 2nd century "preclusive defence" rendered such forts unnecessary . But the existence of such a "strategy" is strongly disputed by several scholars, as many elements of the late Roman army's posture were consistent with continued forward defence. An alternative explanation is that preclusive defence was still in effect but was not working as well as previously and barbarian raids were penetrating the empire more frequently.(see Strategy, below)

Strategy and tactics

Strategy

主条目：Defence-in-depth (Roman military)

Edward Luttwak's Grand Strategy of the Roman Empire (1976) re-launched the thesis of Theodor Mommsen that in the 3rd and early 4th centuries, the empire's defence strategy mutated from "forward defence" (or "preclusive defence") in the Principate to "defence-in-depth" in the 4th century. According to Luttwak, the army of the Principate had relied on neutralising imminent barbarian incursions before they reached the imperial borders. This was achieved by stationing units (both legions and auxiliary regiments) right on the border and establishing and garrisoning strategic salients beyond the borders. The response to any threat would thus be a pincer movement into barbarian territory: large infantry and cavalry forces from the border bases would immediately cross the border to intercept the coalescing enemy army.

According to Luttwak, the forward defence system was always vulnerable to unusually large barbarian concentrations of forces, as the Roman army was too thinly spread along the enormous borders to deal with such threats. In addition, the lack of any reserves to the rear of the border entailed that a barbarian force that successfully penetrated the perimeter defences would have unchallenged ability to rampage deep into the empire before Roman reinforcements from other border garrisons could arrive to intercept them.

The essential feature of defence-in-depth, according to Luttwak, was an acceptance that the Roman frontier provinces themselves would become the main combat-zone in operations against barbarian threats, rather than the barbarian lands across the border. Under this strategy, border-forces (limitanei) would not attempt to repel a large incursion. Instead, they would retreat into fortified strongholds and wait for mobile forces (comitatenses) to arrive and intercept the invaders. Border-forces would be substantially weaker than under forward defence, but their reduction in numbers (and quality) would be compensated by the establishment of much stronger fortifications to protect themselves.

But the validity of Luttwak's thesis has been strongly contested by a number of scholars, especially in a powerful critique by B. Isaac, the author of a leading study of the Roman army in the East (1992). Isaac claims that the empire did not have the intelligence capacity or centralised military planning to sustain a grand strategy e.g. there was no equivalent to a modern army's general staff. In any case, claims Isaac, the empire was not interested in "defence" at all: it was fundamentally aggressive both in ideology and military posture, up to and including the 4th century.

Furthermore, there is a lack of substantial archaeological or literary evidence to support the defence-in-depth theory. J.C. Mann points out that there is no evidence, either in the Notitia Dignitatum or in the archaeological record, that units along the Rhine or Danube were stationed in the border hinterlands. On the contrary, virtually all forts identified as built or occupied in the 4th century on the Danube lay on, very near or even beyond the river, strikingly similar to the 2nd-century distribution.

Another supposed element of "defence-in-depth" were the comitatus praesentales (imperial escort-armies) stationed in the interior of the empire. A traditional view is that the escort-armies' role was precisely as a strategic reserve of last resort that could intercept really large barbarian invasions that succeeded in penetrating deep into the empire (such as the invasions of the late 3rd century). But these large comitatus were not established before 312, by which time there had not been a successful barbarian invasion for c. 40 years. Also Luttwak himself admits that they were too distant from the frontier to be of much value in intercepting barbarian incursions. Their arrival in theatre could take weeks, if not months. Although the comitatus praesentales are often described as "mobile field-armies", in this context "immobile" would be a more accurate description. Hence the mainstream modern view that the central role of comitatus praesentales was to provide emperors with insurance against usurpers.

Luttwak terminates his analysis at the end of Constantine's reign, before the establishment of the diocesan comitatus. Unlike the imperial escort-armies, these were close enough to the theatre of operations to succour the border troops. But their stationing may have differed little from the location of legions in the 2nd century, even though they apparently wintered inside cities, rather than in purpose-built legionary bases. For example, the two comitatus of Illyricum (East and West) are documented as wintering in Sirmium, which was the site of a major legionary base in the Principate.

Furthermore, the late empire maintained a central feature of the forward defence of the Principate: a system of treaties of mutual assistance with tribes living on the imperial frontiers. The Romans would promise to defend the ally from attack by its neighbours. In return, the ally would promise to refrain from raiding imperial territory, and prevent neighbouring tribes from doing the same. Although the allies would officially be denoted tributarii (i.e. subject to paying tribute to Rome, in cash or in kind), in practice the loyalty of the ally was often secured by gifts or regular subsidies from Rome. This practice was applied on all the frontiers. The Romans continued to assist the client tribes to defend themselves in the 4th century. For example, Constantine I's army constructed two massive lines of defensive earthworks, 100–250 km beyond the Danube, totalling c. 1,500 km（932 mi） in length, the Devil's Dykes in Hungary/Romania and the Brazda lui Novac de Nord in Romania. Garrisoned by a mix of Roman and native troops, their purpose was to protect Dacian and Sarmatian tributary tribes of the Tisza and Wallachian plains against Gothic incursions. This created a Transdanubian buffer zone, extending from Aquincum (Budapest) all the way to the Danube delta, obviously contradicting the proposition that the empire's Danubian border provinces were themselves envisaged as buffer zones. This was especially unlikely in the case of these regions, as the Illyrian emperors and officer class that dominated the late army would hardly relish seeing their native provinces reduced to combat zones.

Late Roman emperors continued major and frequent offensive operations beyond the imperial borders throughout the 4th century. These were strikingly similar to the pincer movements described by Luttwak as being characteristic of forward defence in the early Principate. For example, Valentinian I's campaign against the Quadi in 375. Julian in 356–60 and Valentinian I in 368–74 carried out several operations across the Rhine and Danube designed to force the submission of local tribes and their acceptance of tributarii status.

The late army's "defence" posture thus contains many elements that are similar to that of the army of the Principate, raising the question of whether defence-in-depth was ever in reality contemplated (or implemented) as a strategy. But the debate about defence-in-depth is still very much alive in academic circles.

Role of cavalry

Late Roman cavalry officers (bottom right) in a hunting scene. In combat, most cavalrymen would, like infantry, wear a mail shirt and helmet. Mosaic from Piazza Armerina, Sicily. 4th century

A traditional thesis is that cavalry assumed a much greater importance in the 4th-century army than it enjoyed in the 2nd century. According to this view, cavalry increased significantly as a proportion of the total forces and took over the leading tactical role from the infantry. It also enjoyed much higher status than in the 2nd century. At the same time, the infantry declined in efficiency and value in operations, leaving the cavalry as the effective arm. In fact, there is no good evidence to support this view, and plenty of evidence against it.

As regards numbers, the mid-2nd-century army contained c. 80,000 cavalry out of c. 385,000 total effectives i.e. cavalry constituted c. 21% of the total forces. For the late army, about one third of the army units in the Notitia are cavalry, but in numbers cavalry were a smaller proportion of the total because cavalry units were on average smaller than infantry units. For example, in the comitatus, cavalry vexillationes were probably half the size of infantry legiones. Overall, the available evidence suggests that the proportion of cavalry was much the same as in the 2nd century. Examples: in 478, a comitatus of 38,000 men contained 8,000 cavalry (21%). In 357, the comitatus of Gaul, 13–15,000 strong, contained an estimated 3,000 cavalry (20–23%).

As a consequence, most battles in the 4th century were, as in previous centuries, primarily infantry encounters, with cavalry playing a supporting role. The main qualification is that on the Eastern frontier, cavalry played a more prominent role, due to the Persian reliance on cavalry as their main arm. This obliged the Romans to strengthen their own cavalry element, in particular by increasing the number of cataphracti.

The supposedly higher status of cavalry in the 4th century is also open to doubt. This view is largely based on underestimating the importance of cavalry in the 2nd century. Cavalry always had higher status than infantry in the Principate: in the time of Domitian (r. 81–96), auxiliary cavalry was paid 20–40% more than auxiliary infantry.

The view of some modern scholars that the 4th-century cavalry was a more efficient service than the infantry was certainly not shared by Ammianus and his contemporaries. Ammianus describes three major battles which were actually or nearly lost due to the incompetence or cowardice of the Roman cavalry. (1) The Battle of Strasbourg (357), where the cavalry, including cataphracts, were routed by their German counterparts at an early stage, leaving the Roman infantry right wing dangerously exposed. After fleeing behind the infantry lines, it took the personal intervention of Julian to rally them and persuade them to return to the fight. (The cataphracts were later ordered to wear female clothes by Julian as punishment). (2) During his Persian campaign (363), Julian was obliged to sanction two cavalry units for fleeing when caught by surprise attacks (one unit was decimated, the other dismounted). Later, the Tertiaci cavalry regiment was ordered to march with the camp followers for deserting the field just as the infantry was on the point of breaking the Persian line. (3) At the Battle of Adrianople (378), the Roman cavalry was largely responsible for the catastrophic defeat. Scholae units started the battle by an unauthorised attack on the enemy wagon circle, at a moment when their emperor Valens was still trying to negotiate a truce with the Goths. The attack failed, and when the Gothic cavalry appeared, the Roman cavalry fled, leaving the Roman infantry left wing exposed. The Gothic cavalry then routed the Roman left wing, and the battle was as good as lost.

In contrast, the excellent performance of the infantry, both comitatenses and limitanei, is a recurrent feature of Ammianus' history. At the Persian siege of Amida, Ammianus' eye-witness account describes the city's defence by limitanei units as skilful and tenacious, if ultimately unsuccessful. At Strasbourg (357), the infantry showed remarkable skill, discipline and resilience throughout, saving the day at two critical moments.(see Battle of Strasbourg for a detailed account). Even at the disaster of Adrianople, the Roman infantry fought on, despite being abandoned by their cavalry and surrounded on three sides by overwhelmingly superior numbers of Goths.

Tactics

Just as the armour and weapons of the late army were fundamentally similar to those of earlier eras, so the army's tactics were based on traditional principles. The key elements of systematic scouting, marching formation, battle array, fortified camping, and siegecraft were all followed intact in the late period. This section examines aspects of late tactics that differed significantly from tactics of the Principate.

One striking difference was that late army doctrine (and practice) aimed at avoiding open battle with the enemy if possible, unlike the early doctrine from the Principate of seeking to bring the enemy to battle as often and as quickly as possible. The main motivation was likely not a reduced ability to win such encounters. The late army continued to win the great majority of its battles with barbarians. Rather, the primary concern seemed to be the need to minimise casualties. Pitched battles generally resulted in heavy losses of high-grade comitatenses troops, which could not be easily replaced. This in turn supports the hypothesis that the late army had greater difficulty than the Principate in finding sufficient recruits, and especially high-quality recruits. The late army preferred to attack the enemy by stealth or stratagem: ambushes, surprise attacks, harassment and manoeuvres to corner the enemy in zones where they could not access supplies and from which they could not escape (e.g. by blocking mountain passes or river crossings).

Where battle could not be avoided, the late army broadly followed traditional practice as regards array. Heavy infantry would be drawn up in a main line, normally straight and several ranks deep. Mounted archers were stationed, together with light-armed slingers, in front of the main infantry line. Cavalry would be posted on the wings (light cavalry on the outside). Foot archers would form the rear rank(s) of the main infantry line. There would be a reserve line of infantry and cavalry of variable strength, to the rear of the main line, in order to deal with breaches in the main line and to exploit opportunities. At a distance of a mile or so to the rear of the army, its fortified camp of the previous night would contain its assistants and baggage, guarded by a small garrison. The camp could act as a refuge if the army was put to flight. Roman armies in the field never camped overnight without constructing defences. A ditch would be dug around the perimeter of the camp, and the spoil used to erect a rampart, which would then be topped with a palisade of sharpened wooden stakes arranged cross-hatched to form an impenetrable screen. Such defences, systematically patrolled, effectively precluded surprise attacks and enabled the troops to get a good night's sleep.

Where the late army appears to have evolved to some extent is in battle tactics. The older army of the Principate had relied on a barrage of heavy javelins (pila) followed by an infantry charge, which was often sufficient to shatter, or at least disorganise, the barbarian line. After that, legionaries were trained to engage in aggressive hand-to-hand combat, using the gladius short-sword to execute quick thrusts at the abdomen of their enemies, in a similar manner to more recent bayonet drill. In close combat, the Romans had the crucial advantage of superior armour, and such tactics very often resulted in the rout of the less well-equipped and trained barbarian foe. The mounted archers, and slingers on foot, in front of the main infantry line would loose their missiles on the enemy before the infantry lines engaged and then withdraw behind their own infantry line. Along with the foot archers already there, they would continue to rain arrows and sling projectiles on the enemy foot by shooting over the heads of their own infantry. The cavalry's task on each wing was to scatter the enemy cavalry facing them and then, if possible, to encircle the main body of enemy infantry and attack them from the flanks and rear.

In the late army, while the role of archers and cavalry remained similar, the infantry's tactics were less aggressive, relying less on the charge and often waiting for the enemy to charge. During the battle, the Roman line would exert steady pressure in close formation. The thrusting-spear (2–2.5 m long) had replaced the gladius (just 0.5米（1英尺8英寸） long) as the primary mêlée weapon. The extended reach of the thrusting-spear, combined with the adoption of oval or round shields, permitted a battle array where shields were interlocked to form a "shield wall", with spears protruding through the 'V' shaped gaps formed between overlapping shields. The late army also relied more heavily on missiles, replacing the single volley of pila with a more prolonged discharge of javelins and darts.

This kind of combat was consistent with the aim of minimising casualties and its efficacy is illustrated by the Battle of Strasbourg. The battle was primarily a struggle of attrition where steady pressure on the barbarians resulted in their eventual rout. Despite a long and hard-fought struggle, Roman casualties were negligible in comparison to the losses sustained by the defeated army.

The barbarisation theory

Drawing of Flavius Stilicho, the half-Vandal general who was magister utriusque militiae (commander-in-chief) of West Roman forces 395–408. The general is depicted without armour, wearing a chlamys (military cloak) over his tunic and carrying a heavy thrusting-spear and oval shield. He was made a scapegoat for the barbarian invasions of 405–6, although in reality his military skill may have saved the West from early collapse. Derived (1848) from an ivory diptych at Monza, Italy

The barbarisation theory, ultimately derived from Edward Gibbon's 18th-century magnum opus, The Decline and Fall of the Roman Empire, contains two propositions. (1) That the late army recruited much greater numbers of barbarian-born troops than the army of the Principate; and (2) that the greater number of barbarian recruits resulted in a major decline of the army's effectiveness and was a leading factor in the collapse of the Western Roman empire. As discussed above, proposition (1) is probably correct, although it should be borne in mind that probably about three-quarters of the late army's recruits remained Roman-born. This section considers proposition (2).

According to this view, the barbarian officers and men recruited by the late army, coming from tribes that were traditional enemies of Rome, had no real loyalty to Rome and often betrayed her interests, colluding with invading barbarian tribes, especially if those tribes were their own. At the same time, the spread of barbarian customs and culture led to a decline in traditional military discipline, and internal army disunity due to friction between Romans and barbarians. Ultimately, the army degenerated into just a collection of foreign mercenary bands that were incapable of defending the empire effectively.

According to the historian A.D. Lee, there is little evidence to support this view and compelling reasons to reject it. Firstly, the late army clearly was not, and did not become, ineffective. The regular army in the West remained a formidable force until the political disintegration of the West in mid-5th century and continued to win most of its major encounters with barbarian forces e.g. the defeat of Radagaisus in 405. In any case, the Eastern empire did not collapse, even though its army probably contained at least the same proportion of barbarians as the West, if not greater. An analysis of the ethnicity of Roman army officers named in the sources shows that in the period 350–99, 23% were probably barbarian-born. The same figure for period 449–76 officers, virtually all Easterners (as the Western army had largely dissolved) was 31%. In the Notitia, 55 Eastern regiments carry barbarian names, compared with 25 in the Western army.

There is a tendency by some modern scholars to ascribe to ancient barbarians a degree of ethnic solidarity that did not exist, according to A.H.M. Jones. Germanic tribes were constantly fighting each other and even within such tribal confederations as the Franks or Alamanni there were bitter feuds between the constituent tribes and clans. Indeed, a primary reason why many tribal sub-groups surrendered to the Roman authorities (dediticii) and sought to settle in the empire as laeti was in order to escape pressure from their neighbours. The few known conflicts of loyalty only arose when the Roman army was campaigning against a barbarian-born soldier's own specific clan. Ammianus himself never characterises barbarian-born troops as unreliable. On the contrary, his evidence is that barbarian soldiers were as loyal, and fought as hard, as Roman ones.

An indication of the army's high esteem for barbarian-born troops is that they appear to have been preferentially recruited to the elite units of the late imperial era's armies. In the auxilia palatina infantry regiments, the proportion of barbarians in the ranks appears to have numbered anywhere between a third and a half of effectives (compared to a quarter in the army as a whole). From the late 3rd century onwards, barbarian recruitment became crucial to the army's continued existence, by providing a much-needed source of first-rate recruits.

The former Oxford University historian Adrian Goldsworthy has argued that the cause of the fall of the Roman Empire in the West should not be blamed on barbarization of the late Roman Army, but on its recurrent civil wars, which seriously weakened its ability to repel or defeat invasions from outside its frontiers. The East Roman or Byzantine empire on the other hand had fewer civil wars to contend with in the years from 383-432 A.D.

See also

• Battle of Strasbourg
• Historiography of the fall of the Western Roman Empire – article dealing with the Late Roman Empire
• Roman army
  • East Roman army
  • Roman auxiliaries
  • Structural history of the Roman military

References

Ancient

• Ammianus Marcellinus, Roman History (late 4th century)
• Zosimus, Historia Nova (5th century)
• Notitia Dignitatum, Augustana (late 4th/early 5th century)

Modern

• Barlow, J.; Brennan, P. Tribuni Scholarum Palatinarum c. A.D. 353-64: Ammianus Marcellinus and the Notitia Dignitatum. Classical Quarterly. 2001,. New Series, 51 (1): 237–254. doi:10.1093/cq/51.1.237. 
• Bishop and Coulston, M.C. & J.C.N. Roman Military Equipment From the Punic Wars to the Fall of Rome, 2nd ed.. 2006. ISBN 1-84217-159-3. 
• The Cambridge History of Greek and Roman Warfare, vol. 2: Rome from the Late Republic to the Late Empire, ed. P. Sabin, H. van Wees and L.M. Whitby (Cambridge University Press 2007) ISBN 978-0-521-85779-6
• Coulston, J.C.N. (1990) "Later Roman armour, 3rd-6th centuries AD", Journal of Roman Military Equipments Studies, 1 (1990) 139-60.
• Coello, T. Unit Sizes in the late Roman Army. 1996. 
• Cowan, Ross (2015). Roman Legionary, AD 284-337: The Age of Diocletian and Constantine the Great
• Cowan, Ross (2016). Milvian Bridge AD 312: Constantine's Battle for Empire and Faith
• Duncan-Jones, Richard. Structure and Scale in the Roman Economy. 1990. 
• Duncan-Jones, Richard. Money and Government in the Roman Empire. 1994. 
• Elton, Hugh. Warfare in Roman Europe, AD 350–425. Oxford University Press. 1996. ISBN 978-0-19-815241-5. 
• Elton, Hugh. Lenski, Noel , 编. Warfare and the Military The Cambridge Companion to the Age of Constantine. Cambridge University Press CCOL0521818389.015. 2006. 
• Goldsworthy, Adrian. Roman Warfare. 2000. 
• Goldsworthy, Adrian. Complete Roman Army. 2003. 
• Goldsworthy, Adrian. The Fall of the West: The Slow Death of the Roman Superpower. 2009. 
• Hassall, Mark. "The Army" in Cambridge Ancient History 2nd Ed Vol XI (The High Empire 70–192). 2000. 
• Heather, Peter. Fall of the Roman Empire. 2005. 
• Holder, Paul. Auxiliary Deployment in the Reign of Hadrian. 2003. 
• Isaac, B. Limits of Empire. 1992. 
• Jones, A.H.M. Later Roman Empire. 1964. 
• Lee, A.D. "The Army" in Cambridge Ancient History 2nd Ed Vol XIII (The Later Empire 337–425). 1997. 
• Lendon, J.E. Soldiers and Ghosts: A History of Battle in Classical Antiquity. 2005. ISBN 978-0-300-11979-4. 
• Luttwak, Edward. Grand Strategy of the Roman Empire. 1976.  含有內容需登入查看的頁面 (link)
• Mattingly, David. An Imperial Possession: Britain in the Roman Empire. 2006. 
• Nicasie, M.J. Twilight of Empire: The Roman Army from the Reign of Diocletian until the Battle of Adrianople. 1998. 
• Rance, Philip, "Campidoctores, vicarii vel tribuni: the senior regimental officers in the late Roman army and the rise of the campidoctor" in A.S. Lewin and P. Pellegrini (ed.), The Late Roman Army in the Near East from Diocletian to the Arab Conquest ([BAR Int. Ser. 1717] Oxford 2007) 395-409
• Rance, Philip. Sculca, *sculcator, exculcator and proculcator: the Scouts of the late Roman Army and a disputed Etymology. Latomus. Revue d'Études Latines. 2014, 73: 474–501. 
• Southern & Dixon, P. & K. The Late Roman Army. 1996. ISBN 0-300-06843-3. 
• Sumner, Graham. Roman Military clothing (2) AD 200 to 400. 2003. ISBN 978-1841765594. 
• Tomlin, R. S. O. "The Army of the Late Empire" in The Roman World (ed J. Wacher). 1988. 
• Tomlin, R.S.O. (2000), 'The Legions of the Late Empire' in R.J. Brewer, Roman Fortresses and their Legions. Papers in Honour of George C. Boon (London/Cardiff 000) 159-181.
• Treadgold, Warren (1995) Byzantium and Its Army, 284-1081, Stanford: Stanford University Press.
• Webster, G. (1998) The Roman Imperial Army of the First and Second Centuries A.D. University of Oklahoma Press.
• Williams, Stephen. Diocletian and the Roman Recovery. London: B T Batsford Ltd. 1985. 
• Woods, David. Subarmachius, Bacurius, and the Schola Scutariorum Sagittariorum. Classical Philology (University of Chicago Press). 1996, 91 (4): 365–371. doi:10.1086/367528. 

External links

• Diocletian and the Roman Army
• Later Roman Battle Tactics
• The Last Legion
• Champions and Tradition: Single Combat in the Age of Belisarius
• Roman army reenactors
• Comitatus Historical reenactment and Living history group portraying the Late Roman army in northern England
• Britannia Historical reenactment/Living history The largest (and oldest) Late Roman group in the UK, with members located around the country.

Category:Late Roman military Category:Diocletian