A weapon used in the Middle Ages was the trebuchet or more commonly called the Trabuco (Portuguese). Trabuco, which is similar to a catapult, originated in China around 400 BC. The Trabuco was used in the Crusades by the Europeans and was also used in Muslim countries. The Trabuco was used to launch missiles, to either crush masonry walls or shoot a projectile over the wall, using the principle of a lever.
There were two types of Trabucos. A balancing Trabuco and a traction Trabuco. Arab merchants. took the traction Trabuco to the Middle East and redesigned the Trabuco by adding weight to act as a counterweight at the end of a long piece of wood or beam, using gravity as the source of energy to throw the projectile.
The counterweight pulls the beam which casts a large stone or another projectile from a resting point and in a sling, located opposite the counterweight, hurled the projectile, in the same way, that David used a sling to slay Goliath.
The size of the counterweight is directly related to the velocity of the missile. There is documentation on infopedia.pt that a Trabuco threw a 140 pound stone almost to the distance of a football field or 100 yards.
The Trabuco could catapult four stones per minute, which was considered an impressive use of force. The restrictions of this weapon were controlling the number of people to pull on the ropes that had to be pulled down with ropes to release the counterweight to propel the missile or rock.
To achieve four shots a minute the ropes had to be pulled at the same force for each propulsion according to veja.abril.com.br. This type of Trabuco was used to only in the eleventh century.
By the end of the Thirteenth Century, the Trabuco could hurl stones weighing a ton. Animals, such as horses and cows were thrown, as well as human heads and living prisoners were thrown. There was a belief that if infected, diseased human bodies were catapulted, this could spread infections to the enemy. With the advent of gun powder, the Trabuco fazed out of existence.
Learn more about Trabuco: http://www.wordreference.com/pten/trabuco