Casemate
CASEMATE, noun
1. In fortification, a vault of masons work in the flank of a bastion, next to the curtain, somewhat inclined toward the capital of the bastion, serving as a battery to defend the face of the opposite bastion, and the moat or ditch.
2. A well, with its subterraneous branches, dug in the passage of the bastion, till the miner is heard at work, and air given to the mine.