Crenellations are the notched or indented patterns found along the tops of walls, particularly in fortifications like castles. They consist of alternating raised sections, called merlons, and lower sections, known as embrasures. This design allows defenders to shield themselves while providing openings to shoot arrows or firearms at attackers. Historically, crenellations were a key feature in medieval architecture, enhancing both the defensive capabilities and aesthetic appeal of structures. They are often associated with castles, fortresses, and city walls, symbolizing strength and protection in various cultures throughout history.