Trebuchet-A Gravity-Operated Siege Engine: A Study in Experimental archaeology/Vastukaalu Joul Tootav Heitemasin

Article excerpt

Introduction

The purpose of trebuchet reconstructions

Experimenting with trebuchet reconstructions, just as other aspects of experimental 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.

The goal of this paper is to analyse the trebuchet as a mechanical system, and to find the optimal parameters for trebuchet construction and its operation. The reconstructions built by the author and other researchers are then examined from this point of view.

The trebuchet and the progress of technology

The trebuchet consists of a long beam which is attached to a rotating axle. The axle divides the beam into two arms of uneven length. A counterweight is attached to the shorter arm and a sling containing the ammunition is attached to the longer arm. When the trebuchet is cocked, the tip of the long arm touches the ground and the short arm with the counterweight is lifted up. When the trigger is released, the counterweight drops down and the long arm with the sling is pulled up with great acceleration. The sling releases the ammunition at the right moment and it is hurled away towards the enemy (Fig. 1).

[FIGURE 1 OMITTED]

The knowledge of mechanics had to be developed to a high enough level for such a concept to emerge. Furthermore--once these machines were being constructed and used in sieges, their crews and commanders were constantly exposed to the workings of mechanics and previously unsolved issues therein, forcing the brightest minds to contemplate these questions and issues. Thus it is fair to say that the trebuchet has contributed to the progress of science in its own way. One of the most outstanding scholars in the field of theoretical mechanics during the 12th-13th centuries was Jordan Nemorarius (died approx. 1237), who worked on the theory of the lever, based on the principle of the equality of work done and work gained (Piir 1996, 10). Jordan also claimed that a mass falling along a vertical trajectory is capable of doing more work than the same mass falling along a diagonal one. The connection to counterweight-operated trebuchets is obvious here. The trebuchet constructors were aware that a hinged counterweight has a trajectory more vertical than that of a fixed counterweight and thus can fire stones to a longer distance (Chevedden et al. 1995, 63).

Terminology and historiography

The word trebuchet, which is used in English to denote a counterweight operated siege machine, originally meant only the largest and most powerful of these machines. Trabucium, trabuchus, tripantium, trebuchet, etc. are all different forms of the same word. It probably meant 'three legs', referring to the appearance of the machine: bigger machines were supported by two diagonal struts--two legs, while the beam itself depicted the third leg (Chevedden 2000, 100).

The historical aspect of the topic is covered by the 1903 monograph, The Crossbow, by sir Ralph Payne-Gallwey, which has a richly illustrated and commented appendix on catapults. Although the book can be considered obsolete in some sense, it is still of great value. Another important source of information was the manuscript of Ain Mdesalu's yet to be published monograph Ammud, laske--ja heitemasinad muistses vabadusvoitluses ja keskaegses Eestis.

Not many papers have been published in the study of the mechanical aspect of the trebuchet. In the current paper two articles were used, both very thorough but unpublished and available only on the Internet: Trebuchet Mechanics by Donald Siano and The Counterweighted Trebuchet--an Excellent Example of Applied Retromechanics by W. …