 The vulnerability of a structure determined the thickness of the concrete protecting it; the gorge wall of a barrack was thick, while the exposed top of the massif was thick.Protection against infantry was offered by a sea of barbed wire on the glacis around the ditch and the casemates of the gorge, housing 5.7 cm cannons and garrison infantry.These troops were also to be mustered in the massif for a sortie in case of a hostile infantry assault.