How to build a trebuchet.

http://www.ripcord.ws/plans/plans.html

How to build a medieval catapult.

http://www.madison.k12.wi.us/toki/catapult.htm

Catapult Animation watch how a catapult was used.

 http://www.catapultsystems.com/company/funstuff/catapults/animation/default.asp