Ballista

The ballista (Latin, from Greek βαλλίστρα ballistra and that from βάλλω ballō, "throw"), plural ballistae or ballistas, sometimes called a bolt thrower, was an ancient projectile weapon that launched either bolts or stones at a distant target. Developed from earlier Greek weapons, it relied on different mechanics, using two levers with torsion springs instead of a tension prod (the bow part of a modern crossbow). The springs consisted of several loops of twisted skeins. Early versions projected heavy darts or spherical stone projectiles of various sizes for siege warfare. It developed into a smaller precision weapon, the scorpio, and possibly the polybolos.