Crenellation refers to the architectural feature found on the tops of walls, particularly in castles and fortifications. It consists of a series of alternating high and low sections, known as merlons and embrasures, which provide both aesthetic appeal and defensive capabilities. This design allows defenders to shield themselves while firing weapons at attackers. Historically, crenellation was common in medieval architecture, especially in Europe. It is often associated with structures like castles and city walls, where it served to enhance security. The presence of crenellation signifies a building's military purpose and reflects the architectural styles of the time.