battlement
Battlement (noun) means a wall built with regular gaps at the top, from behind which defenders could shoot at attackers.
Etymology
Came into English via Middle English batilment, from Old French bataillement, earlier bastillement ("fortification"), which developed from bastillier ("to fortify, to equip with battlements"), in turn from bastille ("fortress") (see bastion). By surface analysis, it can be read as battle + -ment.