crenulation

Crenulation is a term used in architecture and fortification to describe the pattern formed along the top of a defensive wall or parapet. In this context, it refers to a series of alternating raised sections, called merlons, and gaps or openings, called crenels. The collective arrangement is known as a crenellation, and the wall or parapet bearing it is described as crenellated. The design is intended to provide protection for defenders while allowing them to observe or fire upon attackers through the crenels.

In medieval fortifications, crenulations served both defensive and tactical purposes. Merlons offered cover, and crenels provided firing positions or lookout points. The height, width, and spacing of merlons and crenels varied by region and period, with variations that sometimes included additional features such as machicolations or arrow-slits integrated into the design. Over time, crenellations also gained symbolic or decorative value, particularly in later architectural styles that revived medieval forms.

The term crenulation is also used outside military architecture to describe a margin or edge that is notched or toothed in a similar, though non-defensive, way. In botany, a crenulate or crenate margin describes leaves with small rounded teeth. In geology and paleontology, similar edge patterns may occur on certain surfaces or fossils, where the term conveys a comparable crenated appearance.

Etymology traces crenulation to Latin crenula, a diminutive of creena or crena, meaning notch, with the form entering English via Old French crenelle or crenellation.