A machine used in ancient warfare for throwing stones or darts. It in some measure resembled the cross-bow, but possessed far greater projectile power. It has been thus described: An iron cylinder was fastened between two planks, from which proceeded a hollow square beam, placed crosswise, and fastened with cords, to which were added screws. At one end of this stood the engineer, who put a wooden shaft with a large head into the cavity of the beam; this done, two men bent the engine, by turning some wheels. When the top of the head was drawn as far as the cords would allow, the shaft was driven out of the ballista. The ballista depended and acted upon the same principles as the catapulta, the moving power of which depended on the elasticity of twisted cords, made with women's hair, that of horses, or the entrails of animals. The ballista was usually employed in throwing darts, though, like the catapulta, it sometimes was used in projecting large stones. It is recorded by Vegetius, that the ballista discharged darts with such velocity and force, that nothing could resist their power: and Athenaeus adds, that Agistratus made one of little more than two feet long, which shot darts 500 paces.