There was a show on PBS (I believe) a long time ago that had a bunch of guys recreate a castle siege with a Trebuchet. They built up a large castle wall with local stones and mortor they used in medival times. Then they used nothing but a few hand tools to build larger tools in order to make the trebuchet. I remember one tool they made out of scratch was a lathe to make certain parts of the trebuchet. Pretty cool!! Then they cut out stones, made them round and began their 'attack'. After a few tosses they had it dialed in and knocked the wall down in no time.