Before the invention of the cannon and the introduction of gunpowder as a common piece of military technology, the Trabuco was one of the mainstay pieces of siege weapon technology throughout the known world.
It holds its place alongside the catapult as the weapon of choice for bringing down gates, walls, castles, and any other buildings during the period, as well as for flinging projectiles over the walls to attack the enemies within them. Though a major part of military operations in the western and Mediterranean world, the origins of the Trabuco can be traced back to ancient China sometime around the 5th century BCE according to wordreference.com.
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The Trabuco works under the principle of transference of potential to kinetic energy by way of a fulcrum. Its construction consists of a base of varying size and complexity that has to pieces of wood coming to a parallel point where a long pole is attached in between them. This pole will have a basket or bedding on one end and a counterweight on the other. The height and mass of the counterweight with directly affect the momentum and force of the projectile. The projectile would commonly be composed of stone, wood, dirt, shrapnel, and any other easily available items that could cause injury upon impact. In some cases, corpses were flung over the wall and used as biological weapons as in the siege of Caffa in 1346 CE. Once the counterweight is loosed, gravity will pull it down causing it to swing the pole around culminating with the projectile being flung into the air.
The Trabuco appears to originate from slings used in ancient China. The slings were affixed with long planks of wood to use as a lever increasing the range of the projectiles. By the twelfth century, the Trabuco was a common sight on the battlefield in both Europe and the Mediterranean. A Muslim scholar of the period documents Salamin having knowledge of it and there are accounts from England and France during the same period. By the fifteenth century, the Trabuco declined in popularity and ultimately stopped being used on the battlefield in favor of the cannon.
For more information about Trabuco, just click https://pt.wiktionary.org/wiki/trabuco.