the trebuchet was a priceless item that was used frequently in the 4th century. It was on the same level as the catapult and they both were used for hurling small to large rocks to smash castles and or city walls. The medieval men worked hard on the trebuchet as it was one of the harder designs to make. It was hard to make because it relied on pure balance and because they had non of the technology that we have today they would have to eyeball it. 

the trebuchet was used a lot in Greece and would start havoc within the city because the men that would fire them would fire balls of fire which would start fires almost anywhere. this caused mass production making the trebuchet a widely used siege weapon