A battlement (also called a crenellation) in defensive architecture, such as that of city walls or castles, comprises a parapet (i.e. a short wall), in which portions have been cut out at intervals to allow the discharge of arrows or other missiles. These cut-out portions form crenels (also known as carnels, embrasures, loops or wheelers). The solid widths between the crenels are called merlons (also cops or kneelers). Battlements often have openings between the supporting corbels, through which stones or burning objects could be dropped on attackers; these are known as machicolations. A wall with battlements is said to be crenelated or embattled. Battlements may have protected walkways (chemin de ronde) behind them.