Estonian Journal of Archaeology, 2006, 10, 1, 6180 Tanel Saimre TREBUCHET  A GRAVITY-OPERATED SIEGE ENGINE A Study in Experimental Archaeology The most powerful weapons in the Middle Ages were catapults, the latest and technically most advanced type of which were counterweight-operated trebuchets. This article deals with their mechanics and describes some experimental reconstructions of such siege engines. In Estonia the interest in trebuchets is augmented by the fact that such engines were used here repeatedly at the beginning of the 13th century, during the German-Danish conquest, and thereafter. The author built an experimental reconstruction of a trebuchet and carried out experiments on the Otep hillfort, which resulted in some new knowledge about this type of siege engines enabling us to better interpret the information available in historical sources. Keskajal olid vıimsaimateks relvadeks heitemasinad, mille kıige hilisemateks ja tehniliselt tiuslikumateks tüüpideks olid vastukaalu jıul ttavad heitemasinad ehk blided. Kes- olevas artiklis on ksitletud selliste masinate mehaanikat ja esitletud olulisemaid ajalooliste heitemasinate rekonstruktsioone ja katseid nendega. Eestis on huvi heitemasinate vastu pıhjustanud eelkıige asjaolu, et neid kasutati siin 13. sajandi algul toimunud Saksa-Taani vallutusest peale. Artikli autor on ehitanud blide rekonstruktsiooni, millega Otep linna- mel tehtud katsed annavad keskaegsete heitemasinate kohta uusi teadmisi ja vıimaldavad tılgendada kirjalikes allikates nende kohta esitatud andmeid. Tanel Saimre, Chair of Archaeology, Department of History, University of Tartu, 3 Lossi St., 51004 Tartu, Estonia; tank@ut.ee Introduction The purpose of trebuchet reconstructions Experimenting with trebuchet reconstructions, just as other aspects of experi- mental archaeology, is essential to better understanding our past. The trebuchet is a rather complicated machine and thus its behaviour can be fully understood only through practical experience. On the one hand, this experience helps replenish the information presented in historical sources, and on the other hand complements the knowledge attainable from the modern science of mechanics. Simple high- school level of mechanical analysis can be of much assistance to the historian in developing a sense of criticism towards historical sources.