A wood cut from the painting by Sir E. Poynter showing a torsion powered arrow shooting catapult crewed by roman soldiers and sheltered under a protective shed. This torsion catapult , powered by a twisted skein of rope, or horse hair, is a cross between Archimedes spring engine and a Roman mangonel or onager

The soldier standing at the top of frame is setting the missile, while the rest of the crew draws down the arm. When released, the arm, complete with fist, strikes the missile and sends it off on a ballistic path toward the enemy.