How to Build a Medieval Castle

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Podcast Transcript

Centuries ago, if you were a ruler, you needed to protect yourself and your realm.  You’d obviously need an army and soldiers, but you would also need some sort of defensive fortification to protect yourself from attack. 

The solution to this problem in the middle ages was the development of massive structures which could resist direct attack and often served as a seat of administration for a region. 

Over the centuries, the thought and engineering which went into these structures became one of the highlights of the era. 

Learn more about medieval castles and fortifications and how and why they were built on this episode of Everything Everywhere Daily. 


Let’s suppose you are a medieval lord, king, queen, or someone member of the upper nobility. 

You have a realm you have to protect. You have knights and peasants and a whole bunch of land which is under your protection. You also have rivals who have their own lands and have made some sort of claim against your land. 

You need to both protect yourself and, hopefully, deter any attack from ever happening. You don’t want to appear weak. 

To that end, you decide to build a castle. 

A castle is really just a residence and defensive fortification all in one. A fort or fortification might not have a residence, and something like a palace would not be a defensive fortification. 

For the rest of this episode, I’m just going to refer to the defensive fortifications I’ll be talking about as castles. 

So, you want to build a castle. 

The first and most important thing you have to consider is geography. 

You don’t want to just plop a castle anywhere. You ideally want to build one where the terrain and landscape will do much of the defensive work for you. 

Most castles will be built on hilltops. This allows the castle to have a better view of the surrounding landscape and advanced warning of possible attacks. 

It also ensures that you will always have the high ground if anyone tries to attack you. In times of peace, there is an additional benefit of making the castle visible to everyone in the area, serving as a symbol of strength and security.

If you are more concerned about defense, then you might want to put your castle in an exceptionally well-fortified position. Mont Saint-Michel in France is in one of the best defensive locations on Earth. It is situated on an island in a tidal flat.

Every day when the tide comes in, it is surrounded by water. When the tide goes out, it is surrounded by mud. Anyone attacking by land would only have a few muddy hours to storm the defenses before the tide came in and washed them away. Likewise, if you tried to take the fortification by sea, you’d only have a few hours before your ships were on the ground. 

No one ever successfully attacked Mont Sain-Michel.

Likewise, other castles have been built on the tops of mountains with a single, narrow path leading to their gate. These, too, are near impossible to take, but that doesn’t make it the best option.

If your castle is to be a seat of administrative power, you need people to access it. Sitting on the top of a mountain might not be the best spot if you want to collect taxes efficiently. 

More on this in a bit.

Once you’ve picked your spot, you first need to focus on your outer curtain wall. This is your primary means of defense and, hopefully, the last thing that any attacking force would have to deal with. 

A curtain wall has to be made out of stone. Brick will not suffice as it wouldn’t withstand the force of a massive object thrown by a trebuchet. 

Because large stones had to be quarried and were expensive, most castle curtain walls usually had stones on the exposed inside and outside, and in between, it was usually filled with rubble. 

The two key features that determine the quality of any wall are height and width. 

The higher the wall, the more difficult it would be for attackers to get over it. The thicker the wall, the more difficult it would be for attackers to go through it. 

How high and how thick a wall was built, was a function of time and money. As we’ll see later, castles were enormous investments and took a very long time to build. 

The next thing we need to do is to protect the wall. So long as the wall stands, you are probably in good shape. 

One of the most common means of protecting a wall was with a moat. 

Most people think that moats are designed to keep attackers away from the wall, and this is true. However, the real reason for a moat is to prevent attackers from tunneling under the wall. If you can tunnel under the wall, you can make it collapse, which is difficult to do if you are underwater.

For this reason, some castles actually have moats on the inside of their walls. They still serve the same purpose of flooding any efforts to tunnel under the wall, but they also serve some additional purposes as well, again, as we’ll see in a bit.

Moats were independently discovered in ancient Egypt, West Africa, Japan, North America, and Europe.

You and your people will need to get in, and out of the castle, so your wall will need a gate. 

The gate is the weakest part of any wall, but it is necessary. If you have a moat, that gate will also connect to a bridge, possibly a drawbridge.

This necessitates the construction of a gatehouse. The gatehouse in most castles would be permanently manned, and there would be accommodations inside the gatehouse for guards. 

If there is a bridge over the moat, then at the other end, you might want to build a barbican. A barbican is a small fortification outside the main defensive line that controls the castle’s access.

The outer curtain wall may need to be actively defended, which will means various battlements have to built into and on top of the wall. 

Crennelations are gaps in the top of the wall which allow defenders to shoot at attackers while protected. 

Hoardings are something that were very common in most castles but something you will hardly ever see if you visit a castle today. Hoardings are wooden structures built on the top of walls that would stick out over the edge. 

The hoardings would have holes in the floor, which allowed defenders to shoot straight down at attackers or to drop things on them. 

Permanent stone holes to drop things down were called machicolations.

A hoarding would probably be redundant on a castle with a moat. 

Contrary to popular culture, boiling oil was never used to dump on attackers in Europe. There simply wasn’t any oil, and even other substances like lead were too expensive. Boiling water could do the job just as well. 

You will also need towers along your wall. Towers and turrets could support siege weapons on the top, such as a trebuchet or a scorpion. The tower could also have murder holes or arrow slits to allow defenders to fire arrows or bolts with maximum protection. 

So, we have a really good exterior curtain wall. 

Now, depending on how paranoid you are, you might want to build an interior curtain wall. 

The rules for an interior curtain wall would be the same as for the exterior wall, except everything is probably a bit smaller as it is a second line of defense. 

The total enclosed area is often called a bailey. 

Inside your bailey, you are next going to want to build your keep, sometimes known as a motte. 

Your keep is a defensive structure as well, but it will also have to serve as a functioning building.

Your keep will probably have a great hall where you will hold court and entertain other nobles. It will also have dining rooms, bedrooms, a kitchen, a chapel, and other assorted rooms and offices.

You will probably also want to have a well-fortified storeroom and vault for your valuables. 


While your keep will have a practical function, it will have a defensive role as well. 

For starters, you will probably want the keep to be on the highest section of land and have the highest tower. This will allow you to observe the surrounding area from a safe distance. 

There will be a large door that could be bolted shut if attackers ever made it past the wall. Likewise, murder holes and machicolations will be built into the keep’s walls to shoot down on anyone outside. 

If you ever visit a castle, one of the things you will probably notice are spiral staircases. Most spiral staircases in castles go up in a clockwise direction. 

The reason for this is because a clockwise staircase is easier to defend than one that goes counterclockwise. 

90 percent of all humans are right handed, and this was especially true in the middle ages when lefties were forced to use their right hand. 

In a clockwise staircase, a right handed person defending from above will have their left arm facing the interior of the stairwell whereas the right arm will have more room to swing on the exterior of the stairwell. 

An attacker would have just the opposite problem with little room to swing their weapons. 

Also, stairs would be purposely built with steps with uneven heights. Anyone living in the keep would be accustomed to it over time, but an attacker would be unfamiliar with them and would be more likely to trip and fall. 

So, at this point, you have a wall, a keep, and fortification around your wall and inside your keep. If you have done everything correctly, an enemy probably wouldn’t even bother trying to storm your castle. 

In fact, the storming of castles was a very rare thing in the middle ages. The advantage was on the defender’s side, so attacking could be very costly for the attacker. 


More likely, an enemy would just lay siege to your castle. They don’t have to take it, they just have to surround it and wait you out. 

This means that your castle will need a large supply of food to withstand a siege and a supply of water. 

Before I mentioned that the top of a mountain might not be the best place to put a castle, this is why. While it might be difficult to attack, it is also difficult to escape and supply. 

Many castles were built along the banks of rivers for this reason. The river would provide a natural fortification, but it would also supply water and the potential to bring supplies to the castle if it was under siege. 

If you have adequate defenses, which many castles did, then your ability to withstand a siege was wholly a function of food and water.

Of course, you might want to do more than just sit and take it. You will probably want to fight back or possibly have someone escape to send a message to an ally. 

For this, you might want to put what are known as sally ports into your wall. These are much smaller, easily defended openings where you can send out troops to attack defenders. Likewise, you might also want to build a tunnel that goes far enough away from the castle if you should need to escape entirely.

All of this will probably cost you an enormous amount. In 12th century England, the cost of building a castle would be anywhere from a few hundred pounds for a simple fortification to up to £100,000 pounds….and remember, a pound was an enormous amount of money at that time. 

To put it into perspective, in the year 1270, £10,000 could buy 13,000 horses or pay for a million days wages of skilled craftsmen.

Master James of Saint George, one of the most renowned castle architects of the 13th century, built the Beaumaris Castle in England. He wrote of the construction,

In case you should wonder where so much money could go in a week, we would have you know that we have needed – and shall continue to need 400 masons, both cutters and layers, together with 2,000 less-skilled workmen, 100 carts, 60 wagons, and 30 boats bringing stone and sea coal; 200 quarrymen; 30 smiths; and carpenters for putting in the joists and floor boards and other necessary jobs. All this takes no account of the garrison … nor of purchases of material. Of which there will have to be a great quantity

A decade was not an unreasonable amount of time to complete a castle, and some took much longer than that. 

In 1997, a small group in France began construction of what is known as Guédelon Castle or Chateau de Guédelon.

Guédelon Castle is an actual medieval castle being built with medieval building techniques. It is considered an exercise in experimental archeology. Many of the techniques used at Chateau de Guédelon were adapted for use in the reconstruction of Notre Dame Cathedral after the fire. 

They have been at work for 25 years, albeit with a much smaller team of workers than a 13th-century king would have at his disposal.

Guédelon Castle gets 300,000 visitors annually, and it is a two-hour train ride from Pairs if you ever want to visit. 

Castles served their purpose as a defensive fortification for hundreds of years. What ended their construction was the advent of gunpowder. 

While cannons ended the era of the castle, it didn’t end the era of defensive fortifications. It just changed them to something new called star forts or bastion forts which were specifically designed to protect against cannons. However, I will leave that for another episode. 

There are more than 10,000 castles and ruins of castles in Europe, with probably thousands more around the world in places like the Middle East, Africa, and Asia. Some are enormous and some are small, but all of them tell the story of the people and places where they were built.