Beginning of trebuchet

I have been studying about trebuchets and i've found some very interesting facts. A trebuchet is a type of catapult and it appeared in the 4th century. The word trebuchet is a french word and it is a seige engine. It can also throw five to six times more than the any catapult. The parts that i'm going to learn more about is the trestle, throwing arm, the sling, and the counter-weight.  Here is a picture of two trebuchets. These are some of the most medieval trebuchets i've seen and i got them from  military.discovery.com/.../weapon-07.html.