This is a drawing of a bow style catapult. The bowstrings are pulled taut by the throwing arm. When the trigger is released, the bowstrings pull the throwing arm up and the shot is sent through the air from the cup. A rock can be seen in the cup. Many catapults had wheels to provide easier transportation across the battlefield. Trebuchets, on the other hand, could not be turned or moved once they had been built. The trebuchet crew would move the trough left or right to shoot to the right or left. This was the only way a trebuchet could aim.
