An embrasure (or crenel or crenelle; sometimes called gunhole in the domain of gunpowder-era architecture) is the opening in a battlement between two raised solid portions (merlons). Alternatively, an embrasure can be a space hollowed out throughout the thickness of a wall by the establishment of a bay. This term designates the internal part of this space, relative to the closing device, door or window. In fortification this refers to the outward splay of a window or of an arrowslit on the inside.
In ancient military engineering, embrasures were constructed in towers and walls, in particular between the merlons and the battle. A loophole, arrow loop or arrowslit passes through a solid wall, and thus forms an embrasure of shooting, allowing archer or gunner weapons to be fired out from the fortification while the firer remains under cover.
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