A Good Day for a Trebuchet

15th century depiction of a trebuchet

By Danièle Cybulskie

You know you’re a medieval nerd when you walk into a toy store with the intention of getting toys for actual children, and walk out with a build-your-own-trebuchet kit for yourself. Yep, I spent my Monday night at the kitchen table, constructing a wooden trebuchet. And it’s pretty awesome.

Besides being an especially nerdy way to spend a Monday night, building your own trebuchet makes you think a little bit about how our ancestors must have done it, and what it took to make a working, deadly siege machine. What I found surprising about the trebuchet is its relative simplicity of construction. This makes a lot of sense when you think about it, as trebuchets would have been built (or rebuilt) on the site of an active siege. Although they would have had to be built as far back as possible to avoid being destroyed by the defenders of a castle, there’s only so far you can roll a giant wooden construction, so a quick and easily-built design is essential.


Most of the joints are at angles which would make nailing and/or lashing with ropes relatively easy, and because of its symmetry, the same lengths of wood would be used over and over. This would mean that you wouldn’t need a team of geniuses to make the parts or to put it together – another plus for besiegers (and me). The tricky part would be boring a hole through the throwing arm to allow it to pivot easily, as the arm must be thick and heavy enough to hold the combined weight of both the projectile and the counterweight. This would definitely have been slow work with hand tools.

Once I had built my model, I set about besieging my loveseat – and immediately ran into problems. At first, the projectile (in my case, a little clay ball) didn’t get enough of a swing to launch more than a few inches. A trebuchet, I learned, takes a tremendous amount of weight to launch even a small projectile. I thought maybe several times the weight of the ball would work, but it needed much, much more. In my case, it took an entire container of nails to launch a clay ball; in the Middle Ages, it would have taken more than a tonne of sand or rock to launch a stone the size of a medicine ball. This would have meant a lot of effort for the besiegers: not only would they have had to transport and load all that weight into the trebuchet, but they would also have had to winch up that enormous counterweight high enough to get a good enough swing to launch the projectile. Not an easy task. Also, any miscalculations and recalculations would have had to be done in the field. Needless to say, having a person with experience in charge of the trebuchet would certainly have been a must.


model trebuchetAfter I had done some troubleshooting with the length of the string (it won’t work if the sling attached to the throwing arm is too long), my trebuchet was able to fire its clay ball a good six feet (1.8 metres), which made the nerd in me incredibly happy. What was even better, though, was the consistency and accuracy my little trebuchet achieved, once I had fixed the issues. Each time, the little clay ball hit very close to the same spot, at the same distance. The difference between one shot and the next might have been an inch or two, but in terms of besieging a castle, the difference of a few feet would have been pretty negligible. The ability to hit the same spot over and over again is the key to bringing down a mortared wall, and to have a machine that could be that consistent would have been a game-changer indeed.

The trebuchet’s importance to siege warfare can’t be overstated. Its simple construction, enormous power, and surprising accuracy made it one of the most formidable weapons used in the Middle Ages. One of my favourite books, Fighting Techniques of the Medieval World, recounts the story of a castle in Ibiza surrendering after only ten stones were thrown from a trebuchet (p. 201). It’s not hard to see how intimidating a trebuchet would have been when you see one work, even on a tiny scale. If you’d like to see a replica trebuchet in action, check out this great clip from Battle Castle, or you can watch Hollywood trebuchets in the clip attached to one of my previous posts, Under Siege. To build your own trebuchet, you can watch one of the many YouTube tutorials, or buy the handy kit (like I did) here.

Click here to go to Part 2: The Siege of the Sandpit

You can follow Danièle Cybulskie on Twitter @5MinMedievalist

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