Medieval Siege Tactics

A castle was a well fortified building and when the gates were shut and the drawbridge was raised it was a very difficult place for attackers to get into. Medieval soldiers employed many tactics in their attempts to breach a castle's defences. The term siege is defined as the action employed by an army of surrounding a fortified location cutting its inhabitants off from escape or resupply while being attacked.

The attackers, or besiegers, had several types of siege engines that they used in their attempts to break into a castle, but even with the strongest engine a siege could last months. The attackers sometimes had to wait until the defenders in the castle had run out of supplies and surrendered the castle.

Siege Preparations

The besieging army had to protect itself from attacks from the castle's inhabitants and possibly their supporters outside the castle. It was common for the besiegers to construct two lines of defence around the castle. The first line of defences was built between the besiegers and the castle and was known as the circumvallation. The second line, known as the contravallation, was built around the besiegers so that they were surrounded by defensive walls. Both lines of defence consisted of earth banks and wooden palisades. There was a danger that the besiegers themselves would be besieged within their fortifications. Within these lines the besiegers set up their camps and built their siege engines.

Types of Siege Engine

The Trebuchet

This was the largest of all siege engines. It was designed to throw large rocks and missiles at castle walls to destroy them. Trebuchets came in many shapes and sizes, some having wheels so they could be moved around the siege landscape. Trebuchets were built as kits that could be assembled and disassembled and transported in sections to where they were needed. All the pieces slotted together and were fixed with wooden or metal pegs.

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Siege Towers

The siege towers or belfry was designed to allow attackers to get up over the top of castle walls. The tower had wheels so that it could be pushed up to the castle walls and a drawbridge at the top would be lowered when the tower was in place. To protect the tower from fire it would have been covered with animal hides.

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The Battering Ram

The battering ram was used to destroy the gates or walls of a castle. It would be hidden under a wooden roof to protect the men who controlled it and mounted on wheels so that it could be moved into position.


The Cat

The cat or sow was a wooden shed mounted on wheels. It had a wooden roof angled so that missiles would bounce off and was covered in animal hides to protect it from fire. The cat would be moved up to the castle with men inside safe from attack from the castles walls. This siege machine was used when a section of the moat needed filling in so that a siege tower could be moved into position. It could also be moved right up to the castle so that the men inside could hack away at the walls in an attempt to weaken them.

The Manogel

The mangonel was another siege engine that propelled boulders. It had a throwing arm like the trebuchet but worked on a different principal. The arm was slotted through rope so that when the arm was lowered the rope twisted and provided enough energy to make the arm spring back when released.

Explore a virtual siege

Explore a landscape showing different kinds of siege engine, including the trebuchet, siege tower and battering ram.

Trebuchet Game (Beta Version)

Take control of a medieval trebuchet to destroy the enemy castle and capture their flag.



  • Click the trebuchet or press the space bar to launch the projectile.
  • To get the best result wait for the basket to swing back to the left.
  • The trebuchet will reload automatically after each shot.
  • The game have been tested on desktop IE10, IE11, Chrome and Firefox. It may not work on mobile or other browsers.
  • This game in under development and will be improved at a later date.

Undermining and defending against it

It was possible to destroy castle walls from above the ground using trebuchets and mangonels but it was also possible to bring castle walls crashing down from beneath the ground. The besiegers employed skilled miners who could construct tunnels starting from their camps and ending beneath the castle walls. Under a section of wall the miners would remove the foundation stones replacing them with wooden props. Once enough of the wall had been removed a fire was lit beneath the wooden props and the miners left the mine. When the props burnt through there was nothing holding the castle wall up and it would collapse. The corners of square castles were the weakest part of the construction and this is where the miners would aim to tunnel beneath.

Undermining and defending against it

Tactics to counteract undermining

  • The castle's defenders used a tactic called countermining. This involved digging a tunnel from within the castle to intercept the attackers mine and kill the enemy miners.
  • Castle designers added buttresses and extra projections extending from the walls of the castle. These gave the walls a larger foot print and made them more difficult to undermine.
  • Removing sharp angles from castle designs helped reduce the weak points. Polygonal and round castles were the result of this change in design.

Virtual Reconstructions

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