Gun loop

In military architecture, an embrasure is the opening in a crenellation or battlement between the two raised solid portions or merlons, sometimes called a crenel or crenelle. In domestic architecture this refers to the outward splay of a window or arrow slit on the inside.

A loophole, arrow loop or arrowslit passes through a solid wall and was originally for use by archers. The purpose of embrasures is to allow weapons to be fired out from the fortification while the firer remains under cover. The splay of the wall on the inside provides room for the soldier and his equipment, and allows them to get as close to the wall face and arrow slit itself as possible. Excellent examples of deep embrasures with arrow slits are to be seen at Aigues-Mortes and Château de Coucy, both in France.

The etymology of embrasure expresses "widening".

The invention of the arrowslit is attributed to Archimedes during the siege of Syracuse in 214–212 BC.

From Polybius's (c. 200–118 BC) The Histories:

Archimedes had had the walls pierced with large numbers of loopholes at the height of a man, which were about a palm's breadth wide at the outer surface of the walls. 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.(Bk VIII Ch 5)

However, the invention was later forgotten until reintroduced in the 12th century. See arrowslit.

By the 19th century, a distinction was made between embrasures being used for cannon, and loopholes being used for musketry. In both cases, the opening was normally made wider on the inside of the wall than the outside. The outside was made as narrow as possible (slightly wider than the muzzle of the weapon intended to use it) so as to afford the most difficult possible shot to attackers firing back, but the inside had to be wider in order to enable the weapon to be swiveled around so as to aim over a reasonably large arc.

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