CAPONIER (from the Fr. caponniere, properly a capon cote or house), in fortification, a work constructed in the ditch of a fort so that fire from it can sweep the bottom of the ditch and prevent an enemy from establishing himself therein. The term is used in a military sense as early as in the late 17th cen tury. In various bastioned systems of fortification a caponier served merely as a covered means of access to outworks, the bastion trace providing for the defence of the ditch by fire from the main parapet.