In fortification, a narrow space of level ground, averaging about a foot and a half in width, generally left between the foot of the exterior slope of the parapet and the top of the escarp; in permanent fortification its principal purpose is to retain the earth of the parapet, which, when the latter is deformed by fire or by weather, would otherwise fall into the ditch; in field fortification it also serves to protect the escarp from the pressure of a too imminent parapet.