 Trebuchet at Château des Baux, FranceA trebuchet (also sometimes called a trebucket) is a weapon, a medieval siege engine, employed either to batter masonry or to throw projectiles over walls. The name engine was derived from the Latin word ingenium meaning ingenious device. The word trebuchet is derived from Old French, word trebuchier, to overthrow.
The trebuchet was a development of the Chinese traction trebuchet. In the traction trebuchet a large crew of men pulled down on ropes to propel the missile, in the Trebuchet these men were replaced with a large fixed or pivoting counterbalance weight.
Action of the trebuchet
 Three-quarter view of a trebuchet A trebuchet is moved by a counterweight. The axle of the arm is near the top of a high strutted vertical frame. The shorter arm of the balance carries the counterweight and the longer arm the sling that carries the shot. The sling is usually braided from rope, and has a captive end attached to the arm, and a free end whose loop slips from a hook. A trigger, usually a toggle in a chain, holds the arm down after the trebuchet is cocked. Cocking is often performed with windlasses. Because of the long winding time, a trebuchet's rate of fire was extremely slow, often not more than a couple of shots an hour. Yet some of the smaller types of trebuchets could fire a couple times a minute.
In operation the long, nonweighted end is pulled toward the ground, and held by a trigger. When the trigger is released, the arm pulls the sling out of a channel in the base of the frame. When the ball moves close to the top of its arc, the free end of the sling slips from the hook, and the missile flies free. The trebuchet's arm and frame then oscillate for several cycles.
The efficiency of a trebuchet can be improved by helping the weight to fall more nearly straight down. One method is to place the weight in a swinging or jointed bucket. The sand or stones in the bucket can also be less expensive than fixed metal weights, as well as being easier to gain access to on site. Another trick is to place the supporting frame of the trebuchet on wheels. Either of these improvements can add up to thirty per cent to the overall throwing distance.
Aiming a trebuchet is best practiced with a scale model. Usually small adjustments in elevation can be made by changing the angle of the hook holding the free end of the sling, a process which requires a heated forge on a full-scale engine. For larger, quicker adjustments, the length of the sling can be altered. The perfect release angle is when the missile will fly at roughly 45 degrees, because this optimizes range. After the desired range is achieved, the trebuchet can be moved toward or away from the target. Small adjustments from side-to-side can be made by moving the channel in which the missile and sling slide in the base of the frame.
Trebuchets were capable of reducing cities to rubble as they were able to strike from far away where arrows could not reach their operators. The trebuchets were also able to throw large stones, cows or even shunned negotiators. Rotting flesh (to introduce disease) and barrels of burning tar or oil (to burn the defenders) were also popular. The largest trebuchets had a range of up to a quarter of a mile (400 m). Not surprisingly, the largest of these weapons were not readily transportable and instead had to be built on the spot where they were to be used.
Usage of the trebuchet
The trebuchet is thought to have been invented in China between the 5th and 3rd centuries BC, and reached Europe around 500 AD .
Trebuchets were first used in Italy at the end of the 12th century, and were introduced to England in 1216 during the Siege of Dover.
Due to the increasing popularity of gunpowder, the last historically recorded military use was by Hernán Cortés, whose gunpowder was in short supply, at the siege of the Aztec capital, Tenochtitlán, in 1521. This trebuchet was shot once. Due to a mislocation of the firing pin the trebuchet fired straight up into the air, and its projectile landed on the device, destroying it.
A simulation of trebuchets in action can be seen in the 2003 movie The Lord of the Rings: The Return of the King. The defenders of Minas Tirith fired their trebuchets from the top of the city's battlements. Although this appears very effective, it was never historically used, as castle walls were not big enough to hold a good trebuchet, and the forces exterted by such a siege engine on the walls would destroy them.
Today, people still build and use trebuchets as a hobby. For example, the Punkin Chunkin competition, an annual competition to throw pumpkins for distance, has a trebuchet category. Modern hobbyist trebuchets sometimes replace the counterweight with banks of springs.
The United States organization, Science Olympiad, hosts an event for middle and high school students involving trebuchets. Named Storm the Castle, the competitors build a small trebuchet (maximum one meter square footprint, 75cm high) and fire projectiles at targets.
Variants
A manual trebuchet is called a "stave sling". Basically, it is a sling on the end of a staff. These were the most important form of military sling. They usually shot small lead projectiles called "glans" (Latin for acorn).
If instead of using a counterweight, the spoke is pulled by 2 or more people, the trebuchet is called a traction trebuchet or perrier.
A very recent development is the floating arm trebuchet, where the counterweight drops down vertically .
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