The Trabuco (French: ‘Trébuchet’) is a large weapon of war in the catapult family designed to hurl massive stones great distances to devastate both ramparts and anything inside them. The massively increased range and payload weight over other siege engines represented a technological leap forward in Medieval warfare.
The Trabuco is one of several designs of catapult from the time. All catapults utilize some form of stored energy to propel their projectiles. A ‘mangonel’-style catapult is the most commonly associated with the term ‘catapult’, consisting of a large arm with a bucket or spoon-shaped attachment to the end of the arm to hold the projectile. The arm pulled back, with some sort of energy being stored in a stretched rope. When the arm is released, both it and the projectile swing up, the arm pivoting forward and flinging the projectile towards its target on spanishdict.com. An ‘onager’-style catapult is very similar to a mangonel in design, but instead uses a sling in lieu of a bucket or spoon attachment to hurt the projectile. The ballista, rounding out the family, resembled something like a giant crossbow, launching projectiles that wold be nestled in a sling or pouch and launched straight, rather than via a pivoting arm like the others.
The Trabuco, however, is unlike other catapults according to lista.mercadolivre.com.br. While it does sling a projectile similar to an onager, its energy was stored via a massive counterweight instead of the tension of stretched rope. This enabled it to hurl massive projectiles at distances over three hundred meters, far beyond the capabilities of other weapons at the time. Based on pt.wikipedia.org, given this incredible range, the distance at which an approaching army could begin assaulting a city or castle was extended to far beyond what conventional defenses were prepared for; previously dug moats did nothing and the Trabuco would merely out-range any defenders on the castle walls, effectively striking with impunity.
New, thicker walls had to be built. Larger moats and in greater numbers and range had to be constructed. Counter-artillery in the form of Trabuco within the castle were employed in hopes of driving off enemy forces. The Trabuco became the gold standard of Medieval siege theory, becoming the go-to weapon for siege warfare.
Find more about Trabuco: http://veja.abril.com.br/blog/sobre-palavras/trabuco-da-astucia-ao-chumbo-grosso/