Battlement
A battlement, in defensive architecture such as city walls and castles, is a parapet—a low protective wall between chest and head height—in which regularly spaced gaps or indentations, usually rectangular, allow defenders to launch arrows or other projectiles while the solid sections afford cover. The gaps are called embrasures, also termed crenels or crenelles; a wall or building furnished with them is described as crenellated, while the older synonyms castellated and embattled remain in common use.