Defending a Medieval Castle: The Formidable Features of Some of Britain's Strongest Castles

It’s easy to imagine a Medieval castle under siege - it’s scene that’s been used in tens of thousands of films and TV programmes.

We all visualise images of knights upon horses, charging at mighty grey stone castles. Within the castle, it’s easy to imagine archers firing arrows at the opposition, and residents of the castle pouring boiling oil onto attackers.

Although these images are a bit of an exaggeration, they hold some truth.

Medieval castles were built to be as defensive as possible. Every element of their architecture was designed to make sure that the castle was as strong as it could be, and could hold out against sieges - which could sometimes last months.

Here are the different elements of castle defences which rendered some fortresses truly impregnable.


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Caerphilly Castle concentric designThe concentric walls of Caerphilly Castle, Wales, would have been an incredible defensive advantage.

The Outer Curtain Wall

The ‘curtain wall’ was the vast stone wall which wrapped around the outside of a castle. As you might imagine, it’s called a ‘curtain’ because it covered everything within.

This wall was the main layer of defence, and it tended to be incredibly strong - for example, the curtain wall of Caerphilly Castle in Wales was more than 2 metres (that’s more than 6ft) thick.

Usually, the centre of the wall was made of rough rocks and rubble, and the outer parts were made of gigantic stones, laid like modern-day bricks.

This method of construction gave the ‘core’ of the wall extra strength, and it helped it to withstand battering-rams and missiles.

In Late Medieval times (around 1300s), there was a new innovation in castle building technique - the concentric castle. This was a castle with two seperate layers of curtain walls, one inside the other.

Beaumaris Castle Aerial View Beaumaris Castle is a 'concentric castle' - walls within walls. As you can see, it would be very hard to capture. This photo is reproduced under the UK Open Government License.

Effectively it was ‘a castle in a castle’.

This new design had the strongest defences imaginable, and attackers were barely ever able to capture it. The design can be seen in Wales - a great example is Beaumaris Castle, pictured above.

Moats and Water Defences

Many castles were surrounded by man made ditches which were then filled with water, and turned into moats.

Incidentally, the water in the moat would have been truly disgusting - it was stagnant and all the waste from the castle toilets was tipped straight in.

Caerphilly Castle panorama The moat surrounding formidable Caerphilly Castle in Wales.

However, in Medieval times, everything would have smelled terrible - so the vile moat wouldn’t in itself have put off attackers!

The moat served a number of useful purposes. Firstly, it meant that attackers couldn’t get too close to the outer castle walls. This prevented them from being able to use battering-rams, and made it harder to be accurate when flinging missiles.

It also made it easier for archers in the castle to aim at on-comers. Imagine you were an archer standing on high: if there was someone at the foot of the castle directly below, it would have been too difficult to fire at them accurately. A moat meant that attackers couldn’t get too close - so it was easier to pick them off with arrows.

The moat had other advantages, too. It made it tricky for anyone to burrow beneath the castle, or undermine the outer walls.

Caerlaverock Castle Exterior Another interesting moat is Caerlaverock Castle in Scotland. It has an odd triangular shape, and is surrounded by a deep moat. Credit: John, Creative Commons (CC BY-SA 2.0).

Most moats weren’t actually that deep - usually less than a metre of water. But this was more than enough to foil most attackers. Even if someone were brave enough to wade in, nasty surprises were sometimes hidden deep in the moat - such as sharpened stakes. Ouch!

Turrets, Towers, and Look Out Points

It’s hard to imagine in a world of satellite images, but, in Medieval times, it would have been excruciatingly difficult to interpret where an enemy army might have been marching from.

Castle towers were designed to give an unobstructed panorama of the countryside around a fortress, so lookouts could spot oncoming attackers.

Caernarfon Castle Turrets This is an unusual selection of turrets and towers, part of Caernarfon Castle in Wales. They're partly just for show, but they also command a great view. Credit: Joseph Echeverria, CC-BY-SA-2.0.

Castle architects also realised that, by designing castles strategically, they could glean the best possible view of the surrounding countryside. They therefore designed symmetrical castles - which helped give broader sight-lines - and taller towers, which would maximise the view.

However, armies attacking the castle soon discovered a trick to bring down any tall tower. Castle towers were originally built in a square shape, and so, by burrowing under one of the corners of the square foundations, it was easy to topple an entire tower - and devastate a castle.

The solution? Building round towers, of course! Late Medieval castles boasted circular towers, which had no corners which could be undermined by cunning marauders.

The Gatehouse

It sounds a bit silly to say, but all castles needed an entrance. In times of peace, how else would food, musicians, craftsmen, the Lord and Lady, Knights and nobles ever enter the place otherwise?!

The problem, of course, was that although the entrance to a castle was essential in times of peace, it became the most vulnerable point of the castle during times of siege.

Aerial view of Raglan gatehouse An aerial view of the Gatehouse of Raglan Castle, in Wales.

There would have to be a road up to the entrance - giving the attackers an easy passageway around surrounding obstacles - and, naturally, you can’t build a door out of stone!

This meant that the castle entrance way was very vulnerable to battering rams and flaming onslaughts from any approaching attacker.

The solution to this was the design of the gatehouse. This was an incredibly strong, fortified entrance building that made it really unattractive to attack this part of the castle.

The gatehouse was filled with obstacles - multiple metal portcullis gateways; arrow-slits to fire at intruders; many different gates, doors and drawbridges; and even the infamous ‘murder holes’ - holes in the ceiling which boiling water could be poured through!

The invention of the gatehouse transformed the entrance from being one of the weakest parts of the castle into one of the most formidable spots of all. Would you wish to run the gauntlet of all these of traps and obstacles - or would you find another way to enter the castle?

Some people managed to get through the formidable defences, though, by sheer trickery. In Pontefract Castle, for example, the opposing side managed to get through the siege by pretending to be bed-collectors!

The Drawbridge

Everyone today can imagine a castle drawbridge, but the sort that you’re probably thinking of right now (a large wooden plank, attached to the side of the castle and lowered down on chains) was actually a late Medieval invention - other designs were used for a long time before this.

Bodiam Castle barbican In Medieval times, you'd have found a drawbridge along part of this modern wooden bridge into Bodiam Castle.

Curiously, the earliest drawbridge designs were fussier and a bit harder to explain. At the most basic level, they could just be an unsecured piece of long wood, which was removed when attackers were nearby.

A different system worked a bit like a set of hands on a clock. The wooden drawbridge was rotated across the moat, like a big-hand reaching from 3-o-clock around to 6.

Another system - which we nowadays call the ‘bascule’ - was a see-saw type arrangement, with a complex counterweight on either side to draw one side up whilst the other went down. The remains of one of these can be seen in Raglan Castle, Wales.

The Barbican

During late Medieval times, a further line of defence was built onto threatened castles. This was the barbican - a new extension which jutted out from the gatehouse of fortresses like Dover.

The barbican was an extension of the pre-existing gatehouse. It would have contained another layer of portcullises, murder-holes, arrow-slits and traps to foil attackers.

Reflections of Beaumaris Castle Passageway through the barbican into Beaumaris Castle, Wales. This route contained no less than 15 obstacles - including numerous doors, portcullises, and traps. Credit: Denis Egan, CC-BY-2.0.

Because the barbican was a later addition to Medieval castles, designers understood how to create a truly impassable obstacle. As a result, the only route for anyone walking through a barbicans would have been a narrow path, with many sharp twists and turns.

The reason for so many sharp turns? Well, these turns would have given archers a phenomenal vantage point over anyone walking on the ground. It made any attacker a ‘sitting duck’ - ready to be picked off by a bow and arrow.

Some Incredibly Strong Examples of Medieval Castle Defence

There are some castles you’d never have wanted to have to attack, if you lived back in Medieval times.

Dover Castle is the ‘gateway to England’, and has protected our country from invasion for hundreds of years. It’s has a barbican, a dramatic gatehouse and some formidable curtain walls.

Another mighty castle is Caerphilly in Wales. Caerphilly boasts a vast moat, loads of round towers, and some of the thickest walls I’ve ever seen in my life.

Discover more cunning plots, dusty legends, and tales of England's most beautiful castles...

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And was it a terrible accident, or was Lady Amy Dudley murdered?

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