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 405 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 several 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.

HELIADÉS, in Mythology, the daughters of the Sun and Clymene, according to the poets. They were so afflicted, as they say, with the death of their brother Phaeton, that the gods, moved with compassion, transformed them into poplars on the banks of the river Eridanus.