Urquhart Castle on Loch Ness

The Trebuchet

The trebuchet is a catapult, much used in siege warfare before the development of gunpowder. There are references to them in the literature of China, medieval Europe and in almost contemporaneous Arab literature. One of those involved with the building of this machine had for reference a copy of one such Arab manuscript.

A large trebuchet (the machine before you is only middle-sized) could throw missiles weighing more than 100kg more than 500 metres and with sufficient accuracy to be formidable and effective against fortified positions. This trebuchet can throw a stone ball, like those weighing some 113kg (250 lbs) that you see lying in front of the base, a distance of 180 metres. In so doing, it seriously damaged a purpose-built target wall that stood just over the brow of the hill to the south, where construction work is now taking place.

Power for the throw is generated by the falling counterweight attached to the lower end of the throwing-arm that in this example weighs about 7,000kg. The frame including the axles and wheels are built of green oak. The throwing arm is a Douglas Fir tree trunk some 8.8 metres (29 feet) long cut from the forest on the opposite shore of Loch Ness. Larger trebuchets were also fitted with buckets (rather than having fixed weights), pivoted to the lower end of the arm, into which any suitable and heavy material could be placed to provide the power. This refinement, originating in France, simplified adjustments (in that massive and unwieldy counterweights did not need to be made) since the range was adjusted by filling or emptying the bucket to vary the power. The throwing arm is cocked by suitably rigged ropes and held by a trigger mechanism. Cocking a trebuchet using ropes to draw down the arm required a great deal of manpower, and winches were often used to ease the task.

The direction of the throw can be adjusted either by swinging the whole trebuchet on its base - not an easy task at any time - or, within narrow limits, by angling the missile slide resting on top of the base. The missile in its net sling rests on the slide prior to the throw. On releasing the throwing arm, both are dragged along the slide until hoisted in the air. The moment when the sling is released, freeing the missile to do its work, is determined by the shape of the hook at the top of the throwing arm. Get this wrong and the missile will fly anywhere except sideways or to the target.

Getting the missile’s trajectory just right was time-consuming; much trial and error would have characterised the effort. However, once set up and ranged-in trebuchets were very destructive. The only reliable defence against them was to prevent their construction in the first place. History records that trebuchets were used to throw almost any and every kind of missile that was to hand. Dead animals (especially if diseased) and Greek Fire (burning tarballs) were among the more obnoxious objects used to demoralise and weaken the besieged.

A detailed account of trebuchets in general and of the construction of this trebuchet, and its larger sister now on show at Caerlaverock Castle in the south of Scotland, appeared in the January 2000 issue of The Smithsonian. Assisted by carpenters from this country, both trebuchets were built from raw timber by timber-framers from the US, for the making of one of a series of television films entitled Secrets of Lost Empires by the Boston-based company WBGH/Nova. From delivery of raw timber to firing the missiles took three weeks in October/November 1998. The resulting film - Medieval Siege - is to be broadcast in the UK on Channel 4 TV at 9pm on 1 June 2000. It is recommended viewing - check the transmission time and do watch it (and the four to follow that deal with other related topics)!