The catapult is a device that hurls heavy objects or arrows over a large distance. It was invented in ancient Greece (in 399 BC) by Dionysius the Elder of Syracuse. The Romans later added wheels to the catapult to make it more maneuverable. The catapult (also called the ballista) was a major weapon of warfare for well over a thousand years. A double-armed catapult (also called the trebuchet) was invented by Mariano Taccola,"the Sienese Archimedes." This war machine was invented during the Middle Ages (around 1400 AD) in order to destroy the great walls of the enemy palaces. The trebuchet was designed to throw heavy stones against the walls and simultaneously kill the enemies. The trebuchet was made of wood and iron. This destructive machine was 15m tall and so heavy that hundreds of strong men were required to carry it. The trebuchet has two crates at the opposite side of the basket in which the stone is to be put. The crates are filled with heavy stones so that when the iron rod, which keeps the basket from flying, is pulled out, the crates will fall down and the basket will throw the stone against the enemy walls. If the crates are heavy, then the basket will fly with a stronger force. After throwing the stone, the basket is brought down by the handle on the base of the trebuchet.