Arrowslit

[3] Slits "of the height of a man and about a palm's width on the outside" allowed defenders to shoot bows and scorpions (an ancient siege engine) from within the city walls.

They are reintroduced to military architecture only towards the end of the 12th century, with the castles of Dover and Framlingham in England, and Richard the Lionheart's Château Gaillard in France.

For example, openings for longbowmen were usually tall and high to allow the user to shoot standing up and make use of the 6 ft (1.8 m) bow, while those for crossbowmen were usually lower down as it was easier for the user to shoot whilst kneeling to support the weight of the weapon.

It was common for arrowslits to widen to a triangle at the bottom, called a fishtail, to allow defenders a clearer view of the base of the wall.

[10] Some arrowslits, such as those at Corfe Castle, had lockers nearby to store spare arrows and bolts; these were usually located on the right hand side of the slit for ease of access and to allow a rapid rate of fire.

Inside of an arrowslit, where an archer would stand, at Corfe Castle .
Exterior view of arrowslits in the Bargate gatehouse in Southampton
An arrowslit at Cité de Carcassonne . The wall thickness is reduced to 0.7 m to accommodate the niche and the embrasure widens at an angle of 35°.
An example of a 14th century arrowslit at Hartshill Castle