Roman Ballista

The ballista was a torsion-powered siege and field artillery weapon used extensively by the Roman military from the late Republic through the Empire, adapted from earlier Greek torsion engines. Built around two vertical skeins of twisted sinew or hair rope that stored energy as separate arms were drawn back, the ballista launched heavy bolts or stones along a flat trajectory with considerably greater accuracy and range than a catapult firing on a high arc, making it effective against both fortifications and massed troops in the open field. Roman legions fielded smaller, mobile field versions called scorpiones, giving Roman armies organic long-range firepower that Vegetius and other military writers credited as a significant tactical advantage. The ballista's design, refined over centuries of Roman engineering, remained the basis for Western torsion artillery until it was gradually superseded by counterweight trebuchets and, eventually, gunpowder cannon in the medieval period.