BALLISTA

ancient heavy missile launcher designed to hurl javelins or heavy balls. A smaller ballista was basically a large crossbow fastened to a mount. The huge and complicated Roman ballista, however, was powered by torsion derived from two thick skeins of twisted cords through which were thrust two separate arms joined at their ends by the cord that propelled the missile. The largest ballistas were quite accurate in hurling 60-pound weights up to about 500 yards. Compare catapult.