Polybolos

The polybolos (the name means "multi-thrower" in Greek) was an ancient Greek repeating ballista, reputedly invented by Dionysius of Alexandria (a 3rd-century BC Greek engineer at the Rhodes arsenal,) and used in antiquity. The polybolos was not a crossbow since it used a torsion mechanism, drawing its power from twisted sinew-bundles. However the earlier and similar oxybeles employed a tension crossbow mechanism, before it was abandoned in favor of torsion. Philo of Byzantium (c. 280 BC – c. 220 BC) encountered and described a weapon similar to the polybolos, a catapult that could fire again and again without a need for manual reloading. Philo left a detailed description of the gears that powered its chain drive (the oldest known application of such a mechanism) and that placed bolt after bolt into its firing slot.