Ancient Greece: The Repeating Catapult Of Dionysius Of Alexandria

The repeating catapult of Dionysius was an automatic straight-spring catapult that had the ability to successively fire arrows in a similar fashion to a modern machine gun. The ancient repeating ballista, known as the "multi thrower" or Polybolos was a very impressive achievement for the Greeks. Dionysius of Alexandria a Greek engineer invented this wonder of ancient Greece mechanics during the 3rd century BC. He created the repeating catapult while he was employed in the arsenal at Rhodes. During its time the Polybolos was the most sophisticated catapult ever invented. The catapult's accuracy was not beaten in Ancient Times.

Sadly we aren't sure how widely the Polybolos was used or to what extent the amazing device influenced the future development of similar weapons.

Much of what is known about the Polybolos comes from Philo of Byzantium. Philo witnessed and recorded how a catapult functioned that was very similar to the greek Polybolos.  Philo left a thorough explanation of the gears that operated its chain drive. The way he described the catapult one could easily get the impression he was talking about a conventional machine gun.  For instance, the catapult could fire over and over with no need to reload at any point. It was able to place one bolt after another in its firing slot without interruption. This marks this catapult as the oldest known to use this type of mechanism.

How Did The Polybolos Work? (Animation)

The only thing one has to do is to turn the wheel back and forth. The wheel moves two chains, which in turn moves a slider.

On the slider lies the arrow. A claw keeps hold of the bowstring. The claw lifts, when a joint is rotated. The arrow flies away.

An arrow magazine is attached on top. The arrows make their way through a rotating tray with a cam groove. The tray rotates, when the finger moves back and forth inside the cam groove.

Mechanics Of Repeating Catapult

Gravity-fed arrows from a magazine into the arrow from a spinning drum, to take a shaft at a time. The drum's revolution was regulated by a curved cam groove that held a metal finger on the slider on its exterior. Two flat-linked chains on either side provided the movement for the slider. A  portion of a scientific text detailing the Polybolos helped shed some light on how the catapult might have worked. According to the author of the text, at each end of the belt, the chains went through five-side prisms. The prisms were meant to act as inverted gears.

The chain-link drive used for the cock and shoot process was entirely dependant on the meshing of the chain-link lugs to the pentagonal gear to accommodate the lugs. The rear prism was twisted around by a winch and the bowstring claw was secured and released by the slider-mounted pins in the stock of the weapon. This allows the catapult to automatically fire the arrows until the magazine is bare by moving the winch back and forth.

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