A
battlement in defensive architecture, such as that of
city walls or
castles, comprises a
parapet (i.e. a defensive low wall between chest-height and head-height), in which rectangular gaps or indentations occur at intervals to allow for the discharge of arrows or other missiles from within the defences. These gaps are termed "
crenels" (also known as
carnels,
embrasures, or
wheelers), and the act of adding crenels to a previously unbroken parapet is termed
crenellation. Thus a defensive building might be designed and built with battlements, or a
manor house might be fortified by adding battlements, where no parapet previously existed, or cutting crenellations into its existing parapet wall. The solid widths between the crenels are called
merlons (also
cops or
kneelers). A wall with battlements is said to be
crenelated or
embattled. Battlements on walls have protected walkways (
chemin de ronde) behind them. On tower or building tops, the (often flat) roof is used as the protected
fighting platform.