Battlement

A battlement, in defensive architecture, such as that of city walls or castles, comprises a parapet (a defensive low wall between chest-height and head-height), in which gaps or indentations, which are often rectangular, occur at intervals to allow for the launch of arrows or other projectiles from within the defences. These gaps are termed embrasures, also called crenels or crenelles, and a wall or building with them is described as crenellated; alternative older terms are castellated and embattled. The act of adding crenels to a previously unbroken parapet is termed crenellation.

Quotes

• Others did fortify and rampire their walls, set up little fortresses, bastions, squared ravelins, digged trenches, cleansed countermines, fenced themselves with gabions, contrived platforms, emptied casemates, barricaded the false brays, erected the cavaliers, repaired the counterscarps, plastered the curtains, lengthened ravelins, stopped parapets, morticed barbacans, assured the portcullises, fastened the herses, sarasinesques, and cataracts, placed their sentries, and doubled their patrol.
  • Rabelais, The Third Book of Pantagruel, Author's Prologue, as translated by Thomas Urquhart