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Siege Engines (Trébuchet) @ AEMMA

AEMMA's interest in historical European medieval martial arts also extends to some elements of medieval warfare. A number of senior members expressed an interest in researching medieval "siege engines" or trébuchets. Having worked with the ROM on a number of occassions with collaborative presentations in the past, the ROM had in their possession a traction trébuchet which had raised our interest in this part of medieval military history.
Our interest resulted in the donation of the traction trebuchet from the Royal Ontario Museum (ROM) to AEMMA. We were very pleased and excited over this acquisition and have focused some resource and effort to enhancing our understanding of the physics and history behind the trébuchet. With this in mind, there is no formalized "trébuchet" training program at AEMMA. The trébuchet is brought out on special occassions and events, and the launching of missles is open to all AEMMA students. The trébuchet offers the students a unique opportunity to explore the application of physics with respect to distance, speed, force, trajectory and targeting using an advanced computer program to simulate the trébuchet's behaviour in order to calculate the optimum range, weight and force required to successfully strike a target. Of course, this version of the trébuchet requires raw "muscle" power to operate the trébuchet providing both an intellectual stimulating activity as well as plain old fun!

Trébuchets come in two forms: counter-weight (see images below) and the traction trébuchet (above left and right). Traction trébuchets require human muscle to fire a projectile. The photo above right depicts the trébuchet donated by the ROM.

Brief History by Sir Ralph Payne-Gallwey 1903

This engine was of much more recent invention than either the catapult or the balista of the Greeks and Romans. It is said to have been introduced into siege operations by the French in the twelfth century. On the other hand, the catapult and the balista were in use before the Christian era. Egiclio Colonna gives a fairly- accurate description of the trebuchet and writes of it about 1280 as though it were the most effective siege weapon of his time.

The projectile force of this weapon was obtained from the terrestrial gravitation of a heavy weight, and not from twisted cordage as in the catapult and balista. From about the middle of the thirteenth century, the trebuchet in great measure superseded the catapult. This preference for the trebuchet was due to the fact that it was able to cast stones of 300 lbs. and more in weight or five or six times as heavy as those which the largest catapults could project.

The stones of 50 to 60 lbs. thrown by siege catapults would no doubt destroy towers and battlements, as the result of the constant and concentrated bombardment of many engines. One huge stone of 300 lbs., as slung from a trebuchet, would however shake the strongest defensive masonry and easily break through the upper parts of the walls of a fortress.

The trebuchet was essentially an engine for destroying the defences of a fortification, so that it might be entered by means of scaling ladders or in other ways. From experiments with models of good size and from other sources I find that the largest trebuchets those with arms of about 50 ft. in length and counterpoises of about 20,000 lbs. - were capable of slinging a Stone 300 lbs. in weight to a distance of 300 yards, a range of 350 yards being in my opinion more than these engines were able to attain.

The trebuchet made by order of Napoleon III., and described in his ' Etudes sur l'artillerie,' had an arm 33 ft. in length with a counterpoise of 10,000 lbs. weight to work it. This machine projected a 50 lb. cannon-ball 200 yards, but was so lightly constructed that its full power could not be safely applied.

In a book on ' Experimental Philosophy,' by J.T. Desaguliers, 1734 a curious and interesting old work on mechanical effects, the author gives a detailed calculation of the power of a trebuchet, together with plans of the engine as constructed from the writings of Vitruvius.

These drawings are, however, inaccurate, and though Desaguliers' conclusions are exact, he only allows the trebuchet a counterpoise of 2,000 lbs. which would be far too light a weight to be of any service in an engine of the kind.

The trebuchet is sometimes depicted in medieval books with an arm like that of a catapult (i.e. with a hollow in the end of the arm in which to rest the stone), and without a sling, but this is incorrect.

The trebuchet always had a sling in which to place its missile. The sling- doubled the power of the engine and caused it to throw its projectile twice as far as it would have been able to do without it. It was the length of the arm, when suitably weighted with its counterpoise, which combined with its sling gave power to the trebuchet. Its arm, when released, swung round with a long easy sweep and with nothing approaching the velocity of the much shorter arm of the catapult. The weight of the projectile cast by a trebuchet was governed by the weight of its counterpoise. Provided the engine was of sufficient strength and could be manipulated, there was scarce a limit to its power.

Numerous references are to be found in medieval authors to the practice of throwing dead horses into a besieged town with a view to causing a pestilence therein, and there can be no doubt that trebuchets were employed for this purpose. As a small horse weighs about 10 cwt., we can form some idea of the size of the rocks and balls of stone that trebuchets were capable of slinging. When we consider that a trebuchet was able to throw a horse over the walls of a town we credit credit the statement of Stella who writes "that the Genoese armament sent against Cyprus in 1373 had among other great engines one which cast stones of 12 cwt." Villard de Honnecourt describes a trebuchet that had a counterpoise of sand the frame of which was 12 ft. long, 8 ft. broad, and 2 ft. deep. That such machines were of vast size will readily he understood.


There is no "formalized" regular trébuchet training at AEMMA. Training occurs when an opportunity presents itself to the Academy such as an event in which we are able to assemble and fire the trébuchet approximately once or twice a year.

For details on AEMMA's training program, equipment requirements, armoured tournaments info, and ranking system, click on "training" on the navigation bar at the top of your browser window.


  1. Dr. Peter Vemming Hansen, "Trebuchets", 1994. An online article on the subject.
  2. Dr. Peter Vemming Hansen, "Experimental Reconstruction of a Medieval Trébuchet", Acta Archaeologica vol. 63, 1992, pp. 189 268, Denmark - A resource that describes the reconstruction of the medieval trébuchet which took place in the summer of 1989. It was preceded by over a year's preparations, during which models on scales of 1:10 and 1:5 were built and tried out in combination with studies of the sources. Some elder craftsmen were attached to the project - a smith, a millwright, and a rigger and they interacted with a historian, an architect, an archaeologist, and an engineer in developing the design. In particular the contribution of the craftsmen to research and development were invaluable, and time and again it was found how experience and practical knowledge beat the drawing-board work done, and how often the team returned to the medieval sources and discovered in this long process of trials and errors details that had been missed or gone unnoticed earlier trials.
  3. NOVA, "NOVA Builds a Trébuchet", November 2000 - As seen on NOVA, NOVA and a team of master builders from England, Germany, France and the United States reconstructed one of the most destructive of medieval weapons ever made: a giant trébuchet and fired the missiles within view of Castle Urquhart, located on the shores of Loch Ness in the Scottish Highlands.
  4. Les Scholz, "ATreb" This is a new Trebuchet simulator program, created by Les Scholz, that is rich in features. You can work in either 'Basic' mode to get a quick check or 'Advanced' mode to tweak out those details. You can save configuration data for hundreds of different designs and not have to type in your data everytime. View and print graphs plus a summary of your design. Use aerodynamics, specify all lengths and masses, adjust densities, modify throwing arm cross section, modify friction, select and adjust a propped counter weight, adjust release pin angle, choose between a rotating or non-rotating counter weight, and it even includes an English/Metric unit convertor.
  5. Donald B. Siano, "Trebuchet Mechanics", March 28, 2001 - A 58-page white paper on the subject of physics and mathematics behind the trébuchet by creating accurate simulations using the Mathematica programming language to derive three coupled differential equations from the Lagrangian for the system developed. The physics of the relase mechanism is also described in some detail and the dependence of the range on the finger angle and coefficients of friction. The paper describes the geometry of a full model, including the hinged counterweight and sliding sling.
  6. Donald B. Siano, "WinTrebStar" , April 4, 2002 - Written by D.B. Siano and has been widely used by Trebuchet owners/designers. More commonly refereed to as WinTreb, it is a freebie program and is available at Siano's site: There is a lot of information at his site, so be prepared to spend some time there, it's worthwhile.
  7. The Grey Company Trébuchet Page - A website containing a large amount of information and historical images of "leverage artillery" or trébuchets, traction trébuchets, perriers, petrarias, war wolves, coulliards, bricoles. A good resource for reading up on both historical and contemporary data on this fascinating technology.
  8. Sir Ralph Payne-Gallwey, "The Projectile Throwing Engines of the Ancients", Rowman and Littlefield, 1907 - In this book, Sir Ralph explores the ancient writings of seiges and their artillery. Not content to take the writings at face value, he endeavors to assign credibility to the writer, then he goes on to produce his own working versions of the ancient machines, to test the principles and the claims of the ancient writers.
    Note: This book is a later publication in which the original treatises written on the siege engines can be also be found in the 10th edition book entitled "The Crossbow Medieval and Modern Military and Sporting Its Construction, History & Management with a Treatise on the Balista and Catapult of the Ancients and an Appendix on the Catapult, Balista and the Turkish Bow".
  9. Peter Vemming Hansen, Mag. art.Middelaldercentret, Nyköbing Falster, Denmark, "War Engines of the Middle Ages", a comprehensive online article describing the history of the trebuchet, and the various types that were employed during a siege. The article provides extensive online resources pertaining to trebuchets.

Copyright © 2009 Academy of European Medieval Martial Arts (AEMMA)
Released: July 09, 2003 / Last modified: October 16, 2009