embrasure

An embrasure is an opening in a wall, parapet, or fortification that is designed to allow the operation of a weapon or the passage of light and air. In military architecture, embrasures are openings through which firearms are fired. The outer part of the opening is usually narrow to reduce exposure, while the interior throat is wider to accommodate the gun and gun crew. The sides of the opening may be sloped or beveled to shield the weapon and improve the field of fire. In crenellated walls, the gaps between merlons are embrasures, enabling defenders to observe and fire while remaining protected.

In civilian architecture, embrasures can refer to recessed windows or light wells set into thick walls, especially in historic castles and fortified houses. These openings admit light and air while preserving interior protection, and may be decorative as well as functional.

The term is historical in military contexts and is often distinguished from related terms such as loophole (a narrow firing slit) and gunport (the actual opening through which a projectile is fired).