Polybolos

The polybolos (Greek: πολύβολος, "many missiles" or "throwing many [bolts]") was a repeating ballista, an ancient Greek multiple bolt throwing machine, a type of catapult, believed to have been invented in the 3rd century BC by Dionysius of Alexandria, an engineer working in Rhodes. It is considered one of the earliest examples of a repeating weapon.

The polybolos was significantly more complex than earlier torsion-powered artillery. It was manually operated, with a crank that advanced a slider. The slider performed several actions: drawing back the bowstrings using a ratchet mechanism, loading a bolt from a magazine, and releasing the bolt. This allowed for rapid, continuous firing as long as the operator continued to turn the crank.

Historical sources describing the polybolos are limited, with the primary account being found in the writings of Heron of Alexandria. Heron describes the mechanisms and operation of the device but lacks detailed context regarding its military use or effectiveness in battle.

The polybolos is distinct from other catapults and artillery pieces of the time by its repeating mechanism. While other machines required manual reloading after each shot, the polybolos automated this process, providing a higher rate of fire. This potentially gave it a tactical advantage in sieges and other military engagements, although its effectiveness likely depended on factors such as the skill of the operator, the range to the target, and the accuracy of the device. The complexity of its construction would have made it more expensive and difficult to maintain than simpler artillery pieces. Its use appears to have been relatively limited, and it did not become a mainstay of ancient armies in the same way as other ballistae or catapults.