by Kenneth Daniels

Created on: April 27, 2008

The term "catapult" is a general term for any mechanical device that propels objects through the air. This includes launch systems on aircraft-carriers, a sling shot, a bow, even a clay pigeon launcher for skeet shooting. Let's explore the battlefields of antiquity to understand catapult machines used for warfare.

Terminology and Principles
"Mangonel" is the proper term to use when referring to artillery platforms of the middle-ages. There are three main varieties of the mangonel: The Greek ballista, the Roman onager, and the French trebuchet.

The ballista and the onager are different in appearance, but use the same technology (torsion) to generate energy. Torsion technology is the utilization of sinew (tight ropes) that are stretched or twisted to an extent that when released, will exert massive amounts of force.
The trebuchet however is unique, in that it uses gravity to power a counterweight that is released to propel an object.

The Greek Ballista
The ballista was invented during the 400th century BC in Greece. It was essentially an enlarged version of the hand-held gastraphete (cross bow, or bolt thrower) which was also invented in Greece in earlier 399 BC.
This gastraphete consisted of a bow mounted on a wooden stock lined with a straight metal track. The butt of the stock was fitted with a metal ratchet that would cock the bow into place before loading a bolt or arrow onto the track. When the ratchet was released, the bow would thrust the projectile forward with lethal force.
The ballista utilized this concept of mechanical function on a larger scale.

The body of the ballista was constructed with two retractable wooden arms laid perpendicularly across the front end of a large wooden stock. This unit would be mounted onto a stand that stood upon a platform. The rear end of the stock, fitted with a ratchet device, utilized the torsion system; heavy ropes connected to the arms would be wound back into the ratchet to cock the bow into place. When a spear or rock was loaded onto the track, the operator would release the ratchet, launching the ordnance straight forward.

The ballista could be built atop a wheeled platform for mobility, but the device was mainly intended to be used in stationary defensive positions.

The contraption was rather difficult to operate; the strength of several men was required to stretch the heavy ropes into position prior to firing. However the Greeks eventually upgraded the ballista's design by developing a crank mechanism for the ratchet

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