How medieval castles were actually captured — the siege tactics no one talks about

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Everyone loves a castle. The thick walls, the towering battlements, the drawbridge over the moat. But here’s the question most visitors never think to ask: how did anyone ever actually get inside one?

The answer is stranger, grimmer, and far more fascinating than you might expect.

The castle was designed to make you give up

Medieval military architects were not guessing. Every feature of a castle was engineered specifically to discourage attack. Walls at major fortresses like Bamburgh and Caernarfon ran between three and five metres thick at their base. Arrow loops were angled outward so defenders could shoot in wide arcs while remaining almost impossible to hit.

The gatehouse — always the weakest point — became an engineering obsession. Portcullises, drawbridges, murder holes in the ceiling and bent entrance passages all layered on top of one another. Getting inside without permission was, by design, nearly impossible.

So what did attackers do?

The most common method: just wait

Sieges were not primarily about battering down walls. They were about patience. The most effective tactic in medieval warfare was to surround a castle and cut off its food and water supply. Given enough time, starvation and disease would do the work that no trebuchet could.

Château Gaillard, Richard I’s supposedly impregnable fortress in Normandy, fell to the French in 1204 after a siege lasting several months. The garrison, reduced to a few dozen starving men, had no choice but to surrender. The walls were never breached. The food simply ran out.

This is why medieval castles had wells, grain stores, salting houses, and sometimes livestock pens built inside the walls. The garrison was trying to outlast the besieger — who also faced disease, desertion, and supply problems of his own.

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When patience failed: the siege engine

If starvation was taking too long, attackers brought engines. The trebuchet — a counterweight catapult capable of hurling stones weighing up to 150 kilograms — was the artillery of its age. Well-aimed shots could crack battlements, collapse towers, and shatter the defenders’ morale.

At the siege of Kenilworth Castle in 1266 — the longest siege in English history at nine months — Henry III’s forces used nine massive siege engines simultaneously. The defenders, outnumbered and outgunned, still held out for months. The walls barely budged. Eventually, disease inside the castle did what the trebuchets could not.

Siege engines were also used for psychological effect. Rotting animal carcasses, and occasionally human heads, were lobbed over the walls to spread disease and break morale. Medieval warfare was not squeamish.

Mining: the technique that worked

Of all the methods used to take a castle, mining was arguably the most effective — and the most dramatic. Attackers would dig tunnels beneath a corner tower, propping up the excavation with wooden supports. When the tunnel was large enough, they packed it with combustible material and set it alight. The supports burned away, the tunnel collapsed, and the tower above fell with it.

Rochester Castle in Kent fell this way in 1215. King John’s engineers mined under the south tower and famously used the fat of forty pigs to fuel the fire. The tower corner collapsed exactly as planned, and the breach allowed the royal troops inside.

You can still see the difference today. The south tower at Rochester was rebuilt in a rounded shape after the collapse — round towers being more resistant to mining than square ones. The original square shape on the other three corners remains. History is literally written into the stonework.

The truth about treachery

Here is the uncomfortable truth about medieval siege warfare: most castles that fell, fell because someone on the inside opened a gate.

Treachery was the most reliable method of all. A bribed gatekeeper, a servant paid to poison the well, a garrison soldier who changed allegiance — these were the real threats that castle lords lost sleep over. The famous fall of Kildrummy Castle in Scotland in 1306 came when a blacksmith betrayed the garrison to the English, reportedly in exchange for as much gold as he could carry. He received it — poured molten down his throat.

Negotiation was equally common. Once a besieging force had clearly won the upper hand, the honourable path for a garrison was to surrender under terms: safe passage, lives spared. Medieval warfare had a brutal etiquette all its own.

What to look for on your next castle visit

Knowing how sieges worked transforms a castle visit. That spiral staircase ascending clockwise? It was designed to give right-handed defenders the advantage when fighting down the stairs. Those murder holes in the gatehouse ceiling? Boiling water, not oil — oil was far too valuable to waste.

The moat was rarely water-filled by default. Many were simply dry ditches designed to make it harder to approach the walls and impossible to mine beneath them. A water-filled moat was a status symbol as much as a defence.

Every detail of a castle’s design was an answer to a specific military problem. Once you know what attackers were trying, the defences begin to make perfect, brutal sense.

FAQ: castle siege tactics

What was the most effective way to capture a medieval castle?

Patience — specifically, a prolonged siege that cut off the garrison’s food and water. Most castles fell not to brute force but to starvation and disease over weeks or months. Treachery and negotiation were also extremely common. Direct assault on the walls was rarely successful and enormously costly in lives.

Why do castle staircases spiral clockwise?

Clockwise spirals gave right-handed defenders descending the stairs more room to swing a sword, while right-handed attackers climbing upward had their sword arm pressed against the central newel post. It was a small but deliberate tactical advantage built into the architecture itself.

Were moats filled with water?

Not always. Many castle moats were dry ditches — called “dry moats” or “fosses” — designed primarily to prevent attackers from approaching the base of the walls and to stop mining attempts. Water-filled moats were common in lowland areas where the water table was high, and they did add to a castle’s defensive capability, but water was not the defining feature. The obstacle was.

The next time you stand inside a castle and look up at those walls, remember: you are standing in the answer to a question that soldiers spent centuries trying to solve. Every stone was placed with purpose. Every feature was earned in blood.

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