Polybolos

The polybolos is an ancient Greek repeating bolt-throwing engine, a mechanized development of the torsion-powered ballista credited to engineers working in the Hellenistic tradition of Alexandria in the third century BCE and described by the military writer Philo of Byzantium. Its distinguishing feature was a flat-linked chain drive, turned by a windlass, that automatically cycled a magazine of bolts into firing position, drew the bowstring, and released it in sequence, letting a crew maintain a continuous rate of fire rather than reloading and re-aiming a single-shot torsion weapon by hand between every shot. Ancient sources describe the polybolos chiefly as a fortification and siege-defense weapon, and its chain-driven repeating mechanism is often cited by historians of technology as one of the more sophisticated examples of ancient Greek mechanical engineering applied to warfare, though evidence for how widely it was actually fielded, as opposed to described, is limited.