"Machiolation" explained

A machicolation is a floor opening between the supporting corbels of a battlement, through which stones, or other objects, could be dropped on attackers at the base of a defensive wall. The design was developed in the Middle Ages when the Norman crusaders returned. A machicolated battlement projects outwards from the supporting wall in order to facilitate this.

A hoarding is a similar structure made of wood, usually temporarily constructed in the event of a siege. Advantages of machicolations over wooden hoardings include the greater strength of stone battlements, as well as the fireproof properties.

The word derives from the Old French word machecol, mentioned in Medieval Latin as machecollum and ultimately from Old French macher 'crush', 'wound' and col 'neck'....

The Spanish word denoting this structure, matacán, is similarly composed from "matar canes" meaning roughly "killing dogs", the latter being a reference to infidels.

A variant of a machicolation, set in the ceiling of a passage, was colloquially known as a murder-hole.

Text and image from Wikipedia, via Criminal Wisdom.