Projecting portions of a rampart, so disposed that the bottom of the escarp of each part of the whole rampart may be defended from the parapet of some other part. Their form and dimensions are influenced by many considerations, especially by the effect and range of fire-arms; but it is essential to them to have two faces and two flanks; the former having an average length, according to present systems, of 130 yards, the latter of 40 yards.