A catapult is a device that can fling a projectile, such as a stone, a long way without using explosives. Catapults are large, and are usually moved arond on a cart with wheels. There are various designs of catapult, powered by tensioned rope, sinew or gravity, in the case of the trebuchet. Catapults were used during sieges to break down the defensive walls of castles or used to throw things into castles. The catapult in the picture is a "turn bucket" style, using gravity and a counterweight to fling a projectile.