catapults
...n a wheeled cart so that they could be moved as an enemy changed positions. Some were mounted permanently inside fortresses for defense against attackers. Many different types of catapults were invented and used but the three most common types were the ballista, the mangonel, and the trebuchet. Ballista The ballista used the energy created by twisting ropes to create torsion. The sudden release of this energy was used to launch large rocks, arrows, or flaming balls at an enemy. The earliest catapult was a ballista. It resembled a crossbow and originated in Greece in the 3rd century BC. Engineers working for Philip II of Macedonia, father of Macedonia, father of Alexander the Great, most likely invented the ballista. A ballista used two vertical g...