battlement

Etymology

From Old French bataillement, earlier bastillement (“fortification”), from bastillier (“to fortify, to equip with battlements”), from bastille (“fortress”) (see bastion).

noun

1. In fortification: an indented parapet, formed by a series of rising members called cops or merlons, separated by openings called crenelles or embrasures, the soldier sheltering himself behind the merlon while he fires through the embrasure or through a loophole in the battlement.
2. Any high wall for defense.
3. (poetic) The towering roof of heaven.