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.

The term originated around the 14th century from the Old French word batailler, "to fortify with batailles" (fixed or movable turrets of defence).

Battlements have been used for thousands of years; the earliest-known example is in the palace at Medinet-Abu at Thebes in Egypt, which allegedly derives from Syrian fortresses. Battlements were used in the walls surrounding Assyrian towns, as shown on bas reliefs from Nimrud and elsewhere. Traces of them remain at Mycenae in Greece, and some ancient Greek vases suggest the existence of battlement. The Great Wall of China has battlements