Polybolos 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. Philo of Byzantium encountered and described the polybolos, a catapult that like a modern machine gun could fire again and again without a need to reload. 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.