Embrasure

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).

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.

With the introduction of firearms, the term embrasure designated more specifically the opening made in a fortified structure to allow the firing of these weapons.

Behind each of these and inside the walls were stationed archers with rows of so-called "scorpions", a small catapult which discharged iron darts, and by shooting through these embrasures they put many of the marines out of action.

Another variation of the embrasure featured both horizontal and vertical slits arranged in the form of a cross, and was called a crosslet loop or an arbalestina since it was principally intended for arbalestiers (crossbowmen).

In the 16th and 17th centuries, after the crossbow had become obsolete as a military weapon, crosslet loopholes were still sometimes created as a decorative architectural feature with Christian symbolism.

This allowed for a relatively wide field of fire compared to a traditional embrasure while also minimising the shot trap result created by the sloped opening.

Central-battery ironclads like HMS Hercules featured such embrasures for fore and aft fire from the amidships battery's end guns.