Engineers wage biological warfare---one in three Europeans dead. This medieval weapon replaced the catapult and led to the rebuilding of castles with much thicker walls. Mongols from the orient used the trebuchet in the Crimea against the Genoese. The Mongols hurled dead victims from a plague at their foe: biological warfare. Defeated the Genoese fled back home carrying the Black Death with them. One in three Europeans died.
Those who managed the trebuchet were called "engineers." And the trebuchet required engineers to work properly. For example, there is a story of Cortez's battle with the Aztecs in the siege of Tenochtitlan. The Spaniards built a trebuchet only to have the initial firing send the missile straight up. The trebuchet was totally destroyed, or so the traditional story goes. http://members.iinet.net.au/~rmine/cortez.html
The small scale trebuchet shown above hurls 1/2 inch steel balls with great speed. One of my classes had a great time firing several rounds in the men's bathroom in the basement of the Physical Sciences building. We did this for safety reasons. Note that the green slate blackboards are not slate, but plate glass.
Thanks to Mike Lucas and the Physical Science Machine Shop for design and construction.
The Trebuchet: By: Chevedden, Paul E.; Eigenbrod, Les; Scientific American, Jul95, Vol. 273 Issue 1, p66, 6p, 5 diagrams, 11c.
See also the thorough article by Dr. Donald Siano concerning the physics of the trebuchet. http://www.algobeautytreb.com/