Warlord Marsallas at Pennsic, with a Trebuchet, a medieval catapult of great power and accuracy. Trebuchets were developed in China and came into use in Europe in the 1300,s. They utilized a throwing arm, up to 40 or more feet long, fitted with a heavy counterweight and long line sling. Modern recreations of these machines have shown that they were capable of casting massive objects, up to 1000 pounds in weight, as much as several hundred feet. They were the heavy artillary of the Middle Ages and modern examples have been used to fling cows, pianos and even a VW "Beetle. Roman Ballista and Onager type catapults would have been no match against a Trebuchet.
See photos of the Commander's 1/20 Scale Trebuchet in Action along with more details.