The onager was a post-classical Roman siege engine, which derived its name from the kicking action of the machine, similar to that of an onager (wild ass). It is a type of catapult that uses torsional pressure, generally from twisted rope, to store energy for the shot.
Mangonel Siege engine Catapult Windlass Torsion (mechanics) Spoke Onager Sling (weapon) Ballista Axle Spring (device) Rope Lumber Roman Empire Middle Ages
