Crenels are the notched or indented sections found along the top of a battlement, which is a defensive wall or parapet. These notches create a pattern of alternating high and low sections, allowing defenders to hide behind the raised parts while shooting or observing from the lower sections. Crenels are often seen in historical castles and fortifications, providing both protection and a strategic advantage during conflicts. The raised sections between the crenels are called merlons, and together they form an essential feature of medieval military architecture.