Towers, Movable

The purgi of the Greeks, and the turres mobiles of the Romans, consisted of several stories, furnished with engines, ladders, casting-bridges, etc., and moving on wheels, for the purpose of being brought near the walls. They were usually of a round form, though sometimes square or polygonal. Before the invention of guns, they used to fortify places with towers, and to attack them with movable towers of wood, mounted on wheels, to set the besiegers on a level with the walls, and drive the besieged from under the same. These towers were sometimes 20 stories, and 30 fathoms high. They were covered with raw skins, and 100 men were employed to move them.