The polybolos (the name means "multi-thrower" in Greek[1]) was an ancient Greek repeating ballista, reputedly invented by Dionysius of Alexandria (a 3rd-century BC Greek engineer at the Rhodes arsenal,[2][3]) and used in antiquity. The polybolos was not a crossbow since it used a torsion mechanism, drawing its power from twisted sinew-bundles.[4] However the earlier and similar oxybeles employed a tension crosbow mechanism, before it was abandoned in favor of torsion.[5][6]
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.[7] Philo left a detailed description of the gears that powered its chain drive (the oldest known application of such a mechanism[2]) and that placed bolt after bolt into its firing slot.[citation needed]