in antiquity, a military machine used by the ancients in besieging cities, to throw large stones, darts, and javelins.

It resembled our crossbows, though much larger and superior in force.

From this engine, stones of a size not less than mill-stones, were thrown with so much violence, as to dash whole houses in pieces at a blow. It is described thus: A round iron cylinder was fastened between two planks, from which reached a hollow square beam, placed cross-wise, and fastened with cords, to which were added screws; at one end of this stood the engineer, who put a wooden shaft with a big head into the cavity of the beam; this done, two men bent the engine by drawing some wheels; When the top of the head was drawn to the utmost end of the cords, the shaft was driven out of the ballista, &c.