in the ancient art of war, a machine for battering down the walls of a place besieged, the invention of which is ascribed to Demetrius Poliorcetes.—Diodorus Siculus says, that each side of the Helepolis was 40 cubits in breadth and 90 in height; that it had nine stages, and was carried on four strong solid wheels eight cubits in diameter; that it was armed with large battering rams, and had two roofs capable of supporting them; that in the lower stages there were different sorts of engines for casting stones; and in the middle they had large catapultas for discharging arrows, and smaller ones in those above, with a number of expert men for working all these machines.