A machicolation is a floor opening between the supporting corbels of a battlement, through which stones or material, such as boiling water or cooking oil would be dropped on attackers at the base of a defensive wall.
A smaller version found on smaller structures is called a box-machicolation. Basically, a machicolation is an architectural feature that was used in the defense of castles. The word is derived from a French word – machecol which means ‘to crush’. It is a feature that sticks out from the top of a castle wall or tower from which defenders would drop things.
Later, machicolations were just built for decorative purposes without holes.