Walls have been used for thousands of years during warfare. They are a great way to keep the enemy out and on the other side. Armies first dealt with walls by building catapults which were used to fling rocks at walls in order to collapse them. These worked alright sometimes but they were less than ideal. Catapults were greatly improved upon by the Chinese who designed the first Trabuco. These machines could fling far bigger rocks than any catapult could as well as faster and farther. After further refinements over the course of centuries, Trabuco spelled the end of using walls as fortifications for the most part because they were so effective.
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A Trabuco is s form of a compound machine. Gravity is used to drop a counterweight on one side of a pole. This causes the other end to spring high into the air. Tied to this end is a sling in which whatever you want to fling is placed. During the Middle Ages these slings were usually filled with giant boulders according to dicio.com.br. Sometimes an army wanted to kill the enemy with a Trabuco instead of take down a wall. To do this they could fill the sling with balls filled with flammable liquids to set the enemy on fire. They would also sometimes put the dead bodies of diseased animal in them to hurl at the enemy.
Trabuco’s today are mainly built for education and sport. Physics teachers will build Trabuco to show their students some of the basic concepts of how physics work in the real world. When used for sport people build a Trabuco which they enter into a contest to see who can throw a projectile the farthest. This usually takes the form of a watermelon. However, rebels in Syria did use one for warfare in 2013 during the Battle of Aleppo according to pt.wowhead.com.
Check more about Trabuco: http://pt.bab.la/dicionario/espanhol-portugues/trabuco