Ballista

The ballista (Latin, from Greek βαλλίστρα ballistra and that from βάλλω ballō, "throw"), plural ballistae, sometimes called bolt thrower, was an ancient missile weapon that launched either bolts or stones at a distant target. Developed from earlier Greek weapons, it relied upon 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. Greek and Roman artillery The early ballistae in Ancient Greece were developed from two weapons called oxybeles and gastraphetes. The gastraphetes ('belly-bow') was a handheld crossbow. It had a composite prod and was spanned by bracing the front end of the weapon against the ground while placing the end of a slider mechanism against the stomach. The operator would then walk forward to arm the weapon while a ratchet prevented it from shooting during loading. This produced a weapon that, it was claimed, could be operated by a person of average strength but which had a power that allowed it to be successfully used against armored troops. The oxybeles were a bigger and heavier construction employing a winch and were mounted on a tripod. It had a lower rate of fire and was used as a siege engine. With the invention of torsion spring bundle technology, the first ballistae were built. The advantage of this new technology was the fast relaxation time of this system. Thus it was possible to shoot lighter projectiles with higher velocities over a longer distance. By contrast, the comparatively slow relaxation time of a tension machine such as the oxybeles meant that much less energy could be transferred to light projectiles, limiting the effective range of the weapon. The earliest form of the ballista is thought to have been developed for Dionysius of Syracuse, 400 BC.