A work projecting outward from the main inclosure of a
   fortification, consisting of two faces and two flanks, and so
   constructed that it is able to defend by a flanking fire the adjacent
   curtain, or wall which extends from one bastion to another. Two
   adjacent bastions are connected by the curtain, which joins the flank
   of one with the adjacent flank of the other. The distance between the
   flanks of a bastion is called the gorge. A lunette is a detached
   bastion. See Ravelin.