The trebuchet's name comes from an old French verb for stumbling
Before gunpowder, the mightiest siege weapon was a giant see-saw with a sling. The trebuchet let armies hurl heavy stones at castle walls from a safe distance. Its name grew from an Old French verb meaning to topple or stumble, and the earliest French use described a trap made of balanced logs.
The machine is essentially a lever. A long beam, sometimes 15 metres, pivots on an axle raised high on a sturdy frame. The throwing end is usually four to six times longer than the end where force is applied, and a sling on its tip whips around even faster than the arm, flinging the projectile. Unlike torsion catapults such as the onager, which stop with a violent jolt their frames must absorb, a trebuchet's arm simply keeps swinging and slows on its own. The best ammunition was dense, smooth, rounded stone that would not shatter, sometimes hauled from distant quarries.
The first kind, the traction trebuchet, relied on teams of people hauling ropes. It appeared in China by the 4th century BC, when the Mozi described machines with arms about ten metres long, and spread west, perhaps through the Avars, reaching Byzantines, Persians and Arabs by the sixth and seventh centuries AD. Coordinating dozens of pullers again and again was hard, which limited size.
The counterweight trebuchet solved that by slowly raising a huge box of stones, sand or lead and then letting gravity drop it. Crusader Europe and its Islamic neighbours both adopted it during the 12th century, and the Mongols carried it back east in the 13th, where Chinese writers called it the Muslim trebuchet. The term trebuchet for a stone-throwing war engine appears in French around 1200.
Names remain tangled. Medieval writers used mangonel loosely for almost any stone thrower, so modern historians invented the labels traction and counterweight trebuchet to keep them straight, terms nobody who operated the machines would have recognised.
Source: Trebuchet
