When we place castles on our fictional maps, lots of effort is often made on how to make those castles virtually impregnable. Walls, moats, defensive weaponry etc. But one aspect is often overlooked in fiction: How much use is my super-strong castle really?

The purpose of a castle is to

  • protect people and goods inside
  • stop travellers and armies passing by
  • project power over the surrounding land

As to the first point: sure I can escape into my eagles nest and be relatively safe as long as supplies last. But unless I have a sizable force at my command, this only means I imprisoned myself. Really, this means using up lots of resources just to postpone an inevitable defeat scenario. A paranoid tyrant might build one, a wise general would not. Note, I'm talking "pure castles" here. Walled cities are certainly useful where bandits roam, but typically no way near as strong as a castle.

The second point is very valid if my castle is placed at a strategic chokepoint, a bridge/ford or a pass. It makes a hostile invasion very costly since the castle must be taken for the army to pass. But unless I have such choke points, the value of a castle drastically lessens.

Finally to projecting power. It is not really the castle that does this, it's the garrison. The main advantage which a castle gives is that my soldiers can rest protected inside, while any insurgents outside always must be alert. This only works against an inferior force though. If the enemy has set up camp close to your castle (but out of range) your soldiers are quite useless. He does not need to storm the castle, since time is working in his favour.

So, to the question: Obviously castles were deemed useful in the real world, so they do have merits.

Is there a good reason to build really tough castles unless their position is very strategic? How can I make it necessary for an opponent to storm my super strong castle rather than just passing by just out of range (leaving a small guard to keep the defenders inside)?

Tech level/magic should be quite unimportant here. There is a certain range outside which defenders cannot attack from within the castle. An attacker can besiege or storm a castle, but storming would mean heavy losses.

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    $\begingroup$ They can produce little castles? $\endgroup$
    – dot_Sp0T
    Commented Aug 17, 2018 at 8:44
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    $\begingroup$ Tech level/magic is very important. If you can helicopter in/out via the roof or magic up new provisions then this Problem changes entirely. $\endgroup$
    – Joe Bloggs
    Commented Aug 17, 2018 at 8:47
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    $\begingroup$ Defence in depth and Hedgehog defence might interest you. A useful historical example is the Burhs in England, which gave logistical and reinforcement advantages to the English mobile forces, performed counter attacks and logistical disruption on the attackers, prevented the attackers capturing a town and just sticking around, blocked strategic waterways and reduced the economic rewards of opportunistic raiding/invasion. But impregnablity isn't a must here. $\endgroup$
    – Nathan
    Commented Aug 17, 2018 at 9:49
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    $\begingroup$ A relevant question from the History SE: Why bother attacking castles at all. More from the attacker's POV than the defender's, but still relevant. $\endgroup$
    – user52733
    Commented Aug 17, 2018 at 20:52
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    $\begingroup$ Just noting, but a mountainous country like Slovakia has around 1 military castle for every 20 000 modern day inhabitants. A flat country like the Netherlands has 1 military castle for every 300 000 modern day inhabitants. Sure, those numbers are very very very rough, but the point is that castles are a LOT less useful when a country doesn't have choke points. $\endgroup$ Commented Aug 18, 2018 at 0:11

16 Answers 16


TLDR: It's a matter of cost: building castles costs a lot, but assieging a castle also costs a lot. However, you need to control the castle in order to secure your supply line and/or control the region.

As to the first point: sure I can escape into my eagles nest and be relatively safe as long as supplies last. But unless I have a sizable force at my command, this only means I imprisoned myself. Really, this means using up lots of resources just to postpone an inevitable defeat scenario

Thing is, sieges cost more for the attacker than the defender. You have to outnumber the defender if you want to assiege him properly, either by force or with time. So, yes, you will consume food and water, but so the enemy. And while you have lot of cereals, dried meat and stuff in your castle and have to feed a small garrison, the enemy has to forage in the countryside to feed a tenfold larger army.

But unless I have a sizable force at my command

Both your army and your castle match your power. You can't have an impregnable castle if you are a petty count. You can assume that someone who can afford and maintain a castle, whatever his size, can also handle a garrison.

The second point is very valid if my castle is placed at a strategic chokepoint, a bridge/ford or a pass. It makes a hostile invasion very costly since the castle must be taken for the army to pass. But unless I have such choke points, the value of a castle drastically lessens.

As you said, if the enemy army needs to control the castle in order to go beyond the castle, such a castle makes sense, but I disagree that the value of a castle drastically lessens otherwise: if he didn't want to go beyond that castle, it means the enemy wants to control your region. Again, in this case, a castle makes sense.

Finally to projecting power. It is not really the castle that does this, it's the garrison. The main advantage which a castle gives is that my soldiers can rest protected inside, while any insurgents outside always must be alert. This only works against an inferior force though. If the enemy has set up camp close to your castle (but out of range) your soldiers are quite useless. He does not need to storm the castle, since time is working in his favour.

Having a castle is really great to harass an army, either by attacking the rear, or even better, cutting the supply line. Military logistics such as "how to feed an entire army, several km away from its country" are often underestimated.

And if you are the inferior force, good for you. As stated before, it will cost the enemy much more than you, and some sieges can last for several years.

How useful is an impregnable castle? Tremendously useful. However, not everyone could build one. It's a common fantasy trope to build a much bigger castle than historical ones; it's up to you to see how big castles are in your world. But they will be useful

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    $\begingroup$ I think you should include the "attach the supply lines if they go past the castle" bit in the TL;DR. That's the main reason why a castle left unconquered is a threat, and without it the current tl;dr point of "it costs a lot to conquer it" is kinda pointless. $\endgroup$
    – Syndic
    Commented Aug 17, 2018 at 12:18
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    $\begingroup$ For the first point it is important that while you may not have an army to match the opponent (otherwise you'd have engaged them head on instead of retreating to a castle) you hopefully have allies (or a king above you). But since armies only moved at walking pace in middle ages, it will take them long to amass the army and come to your help. A good castle lets you survive until the help arrives. $\endgroup$
    – Jan Hudec
    Commented Aug 18, 2018 at 14:59
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    $\begingroup$ @Syndic That's assuming there are supply lines to be concerned about, though, which was not the norm for ancient times. Hannibal cut through several roman fortifications without bothering to conquer them, because his army had to survive by foraging the local terrain, as it was the norm in those times - Alexander the Great didn't have the food sent by from Macedonia. It's true he risked being attacked from the back, but he didn't care - actually, he ambushed the roman forces which chased him at the battle of Lake Trasimene. $\endgroup$
    – Rekesoft
    Commented Aug 20, 2018 at 9:50
  • $\begingroup$ @Rekesoft warfare in antiquity was however quite diferent, with much bigger army, and no castle (or at least not like the middle age ones), they besieged whole cities. And it was the lack of supply lines, among other things, that destroy the army of Hannibal: as it was too risky to make a propper battle, romans used guerilla tactics. $\endgroup$
    – Kepotx
    Commented Aug 20, 2018 at 10:00
  • $\begingroup$ @Kepotx True. The Hannibal "supply line" was exceedingly large, that's why Hannibal defined his strategy without counting on it. In the end, however, his strategy of fomenting rebellion among the italic nations subdued by Rome was a failure. $\endgroup$
    – Rekesoft
    Commented Aug 20, 2018 at 10:03

Castles were useful for a certain type of defensive warfare. They allow you to project power over an area with a relatively small but immobile force. You could consider them to be primarily a delaying tactic, designed to hold up the enemy until such time as a significant force could be brought in.

A good castle can be the deciding factor when a smaller force is defending against a larger one. If you have a larger force and a castle, then you don't retreat to the castle, you engage in battle.

Some groups decided that castles weren't so useful, during one of the Scottish rebellions they realised that for their style of highly mobile combat, castles were a trap. They demolished any that they took.

Remember that the difference between an impregnable fortress and an inescapable prison is the side of the doors that the locks are on. Or in the words of the immortal General Callus Tacticus (Terry Pratchett):

After the first battle of Sto Lat, I formulated a policy which has stood me in good stead in other battles. It is this: if the enemy has an impregnable stronghold, see he stays there.

If you have retreated to your castle with a larger force then the attackers should do their best to ensure that you remain inside.

In extremis you play the siege game, where the stores of the castle are played off against the logistics of the attackers, but you really don't want to do that if you can possibly avoid it. If your force is too small and the enemy large with good logistics, your castle will become your prison, and ultimately your grave.

Kings build castles, they're a statement, a fortress, a garrison, an armory, a prison. These things are all useful in their place.

Generals do not build castles, they want to be mobile.

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    $\begingroup$ "in the words of the immortal General Callus Tacticus" - I'm pretty sure he died. Probably of old age. You may have meant "in the immortal words of the General Callus Tacticus"? $\endgroup$
    – AndyT
    Commented Aug 17, 2018 at 11:20
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    $\begingroup$ Note that the siege game gives a head start to the inhabitants of the castle. Logistics, in the Middle Ages, were hard: there were few good roads. A castle can have deep stores, and as the enemy approach food can be moved into the castle (or burned) leaving the besieging foe having to haul food from a long distance and making maintaining the siege a very costly proposal. That's a small force entrenched in the castle can "defeat" a large force: cut off access to immediate resources, forcing retreat to controlled lands. $\endgroup$ Commented Aug 17, 2018 at 13:05
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    $\begingroup$ @AndyT I was reading that book last month and he was still alive then. I lost the book, so he will never die. $\endgroup$ Commented Aug 17, 2018 at 13:07
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    $\begingroup$ @AndyT: "Do you not know that a man is not dead while his name is still spoken?" $\endgroup$ Commented Aug 17, 2018 at 17:55
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    $\begingroup$ @ArcanistLupus “I don't want to achieve immortality through my work; I want to achieve immortality through not dying. I don't want to live on in the hearts of my countrymen; I want to live on in my apartment.” $\endgroup$
    – Michael
    Commented Aug 19, 2018 at 16:37

Standing army is expensive. Both in money and in supply. Any medieval lord had a very limited amount of resources at their disposal at any given moment in time. Combined with the terribly inefficient logistics of the time, in most cases they just can't afford to keep the army in the field for a prolonged period of time.

For instance, in 1066 king Harold effectively crushed the Norwegians at Stamford Bridge, but had to disband his army immediately after that (even despite the ongoing Norman invasion!) as he was not able to keep the army supplied for long enough.

While sitting inside your fortifications, you slowly spend your resources. Your enemies, however, spend their resources at a much higher rate as they have to keep a larger force in the field.

This means that you don't need to sit in the safety of your eagle's nest forever. You just need to wait until their vassals get tired, their coffers get empty from paying mercenaries for just being there, their soldiers start to desert in masses because of hunger and diseases, which will inevitably spread in their camp as they have no idea of sanitation. And this will happen very soon.

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    $\begingroup$ Interesting. I simply assumed that an invader could let his army pillage the country and thus would have the advantage. $\endgroup$
    – Guran
    Commented Aug 17, 2018 at 10:07
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    $\begingroup$ Technically the Normans did not actually invade until 3 days after the Battle of Stamford Bridge and with 11th century communications it would have been a few days after that Harold 200 miles away in York knew of it. $\endgroup$
    – Sarriesfan
    Commented Aug 17, 2018 at 10:46
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    $\begingroup$ @Guran: You assumed there was anything worth pillaging. However, the same rule works for castles and safes: valuables should be in. It would be a tremendous tactical mistake to leave good food outside the castle when the enemy approaches: either bring it into the castle or burn/spoil it. Leave nothing to the enemy, force them to stretch their supply lines over miles and miles. And if you are in position to harry them, aim for the food stores/supply lines => an army marches on its stomach! $\endgroup$ Commented Aug 17, 2018 at 13:11

Castles were built in strategically relevant locations for exactly the same reason you point out: physically control a road, a river, a border, a lake when there are little or no alternatives for an ill intended opponent.

And that was also the reason why they were often dismissed: once the strategic reason is removed, they become a monetary bleed.

So, no, nobody sane would build a castle in a location with no strategic relevance. If you cannot force your enemy to attack the castle, you cannot use the castle to chase your enemy.

If instead the military usage is not the main scope of the building, the location can be chosen at leisure: see Castle Neuschwanstein.

  • $\begingroup$ Ludwig II built the best castles. All of them useless, but all beautiful. $\endgroup$
    – Separatrix
    Commented Aug 17, 2018 at 9:29
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    $\begingroup$ German has two different words for "castle", the first being "Burg" for a building that focuses on fortification, and the second "Schloss" for a building that focuses on splendor but which might have some fortifications as well. No German would call any of Ludwig II's creations Burg. $\endgroup$ Commented Aug 17, 2018 at 15:27
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    $\begingroup$ In English, the two words would be "Fortress" and "Palace." They aren't quite as linked to "Castle" as Burg and Schloss are, but they are close. Ludwig II built palaces. Absolutely beautiful though. $\endgroup$
    – NomadMaker
    Commented Aug 18, 2018 at 21:38
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    $\begingroup$ @NomadMaker Pedantically, the word “palace” came from the name of a hill in Rome. The word “castle” comes from a description of the style of crenelations along the tops of the walls. $\endgroup$ Commented Aug 19, 2018 at 6:09

Castles are useful for defense of the land. It's really hard to take over a piece of land if, in the middle of the night, you could get slaughtered by soldiers whose entry you couldn't prevent because they live there. They're already on the land, so you can't keep them out. You can't drive them out, because they can retreat to their castle, which is a privilege you can't afford. You can try to take the castle, but that will inevitably lead to problems.

You can hold out for a long time in an impregnable castle. Plenty of food, a source of water and any other provisions mean that it would be incredibly costly to try to take over your territory. An attempt to overwhelm the castle quickly would be stupid: you could murder them from above while they hammer away ineffectually at the walls.

If you want to take over somebody's land, you basically have to take the castle- otherwise you'll have to perpetually defend against its soldiers. An impregnable castle makes this very difficult.

Also, imprisoning yourself inside the castle means that nobody is working the land. The entire region shuts down and becomes useless.

A strong castle is a way of concentrating all the value in a large, indefensible area into one impregnable stronghold so that it can't be stolen. The knowledge that this would happen is enough to deter would-be invaders.

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    $\begingroup$ Good answer. Can you add something regarding the "range" of a single castle? Is it realistic to state that a castle roughly controls land as far as a strike force from the garrison can reach, fight and return within a day? $\endgroup$
    – Guran
    Commented Aug 17, 2018 at 9:03
  • $\begingroup$ If you have already taken the land then there won't be a constant stream of soldiers from the castle. They are bleeding out. They do not get supplies anymore. At that point you have already won. If the enemy is hiding in a castle that is not in strategic position instead of defending their land it is over. $\endgroup$ Commented Aug 17, 2018 at 9:03
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    $\begingroup$ @ArtificialSoul You take the land, start some farmers working there. That night, 6 horsemen exit the castle, ride down to the farms and kill the farmers, go to the supply wagons of your soldiers and set them on fire, then hunt down any running foot soldiers before returning to the castle just as your main force is being assembled. You can't keep your soldiers perpetually awake- the castle has the advantage of safe nights and the ability to choose when the fighting happens. When you take away supplies, they don't die immediately. Castles are built to withstand siege. $\endgroup$ Commented Aug 17, 2018 at 9:13
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    $\begingroup$ @ArtificialSoul Yeah, there's always the possibility of a shift-scheduled siege system. But at that point you're spending more resources keeping the castle in check than you'll get from the land in a year, and it's no longer a quiet takeover while the lord locks himself in the castle: it's a full on siege. That's kind of the point of a castle - a costly siege is the only way to gain access to the land. Also, the garrison isn't a thousand soldiers- it could be just 20 horsemen and 20 men-at-arms working as guards. A castle reduces the need for manpower. $\endgroup$ Commented Aug 17, 2018 at 10:12
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    $\begingroup$ @ArtificialSoul Those 40 men hold the castle, harass your supply line etc whilst they wait for the King and his Lords to assemble an army to relieve you. It's what happened throughout English history (which is what I am most familiar with) for example the Siege of Lincoln they French Prince Louis besieged the castle until an English force lead by the Earl of Pembroke mustered and attacked them. It's a secondary affect of castles they can fix attacking forces in place whilst you gather your troops to respond to an attack. $\endgroup$
    – Sarriesfan
    Commented Aug 17, 2018 at 10:54

Walking around the castle has its costs

As you mentioned the enemy has an option to simply walk around, however if they do so they dont have much of a choice in leaving force strong enough to keep your garrison inside. If your garrison was allowed to roam freely, they could disrupt the supply lines, which is something you dont want to allow.

There are high requirements on such force - first of you need to outnumber the defenders 3 to 1, preferably 5 to 1 in order to discourage defenders from trying anything. In addition you need some men to pillage the country to keep the siegeing force supplied. There is also the requirement of at least decent morale and loyalty - you dont want all of your soldiers to wander off to pillage giving defenders option to overpower the spread out forces.

If you had a dozen castles

If the bulk invading army consisted of 30 000 men and you had 12 castles with garrison of 200 men each, your castles could lock easily total 10 000 of the invading force in stalemate below their walls. Easily doubled if you had the time to reinforce said garrisons.

In addition, having a multiple of castles on the way to your capital would significantly weaken the main force not just numerically. Main force would be more vulnerable as any of the besieged garrisons could find a way to get rid of the attacker at any point of time (a distant vassal coming to help) flanking the main army, disrupting supply lines, freeing other garrisons or finding any other way to make main army life more complicated.
Another consideration is they cant just leave the pleb guarding your garrisons - as mentioned above they would most likely wander of plundering countryside. Fair share of the force left behind would need to high morale units with minor commanders with them making the numeric loss even more significant.

  • Castles as Fortified Garrisons
    Some castles would be built to hold down the population of a restive province. They provide a base for the "occupation" forces sent by the "central" government or by a foreign power. A strong castle can be held by a relatively small garrison, so once you have built it the mobile forces can either be reduced or sent out on patrol.
  • Castles as Fortified Manors
    Some castles were built by a local ruler to protect his property and that of his subjects against intruders or serf uprisings. In a castle, a relatively small garrison could defend the household of the lord and possibly even the serfs and their livestock.
  • Castles to hold Chokepoints
    There was some of that, but a castle could not project power beyond the range of a catapult or early cannon unless it also had a mobile force, which would make this the first bullet point. A somewhat related issue might be castles as bridgeheads, when one end of a bridge or perhaps both are fortified. But that't not an independent castle, more an outer works for the city on the other side of the bridge.

So castles have the same purpose as the much-maligned Maginot Line. They allow a small permanent garrison to hold a larger enemy off until more of the own forces can be mobilized.

  • The Defender has Height and Cover
    When most weapons are muscle-powered, standing on top of a high wall has distinct advantages.
  • The Defender has Interior Lines
    That means the besieger might need more troops to circumvallate the castle than the defender needs to hold it.
  • The Defender has Housing and Supplies
    Sure, a castle under siege is not a healthy place to live, but a medieval field camp is even more unhealthy. More besiegers than besieged might starve and get sick. Also, armies marched much slower than a single messenger. So the defender probably had time to gather extra supplies from the outlying villages, while the invader has to bring them over a long distance -- all nearby supplies were moved into the castle.
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    $\begingroup$ Indeed, the housing part is very important. Even in peace time, a castle is useful to house your troops. You can't have a permanent defence force without somewhere to house these, and they won't be happy and ready for war if they must wait in a muddy plain. $\endgroup$
    – Kaël
    Commented Aug 17, 2018 at 16:18
  • $\begingroup$ @Kaël, if it was just about having shelter, a manor without walls would do. Castles are a fortification that doubles as living space, or vice versa. $\endgroup$
    – o.m.
    Commented Aug 17, 2018 at 16:30

You want your enemy to try storming your very strong castle even if it is not strategically placed, or at least you need to gain something by building that huge and strong fortress.

But castles are not only useful for this. First, understand your super strong castle controls your territory. Your enemy may destroy whatever it likes and plunder every village on the way to your castle.... yet, the territory will not belong to him while there is that super strong fortress and its garrison inside it. His peasants will never have the opportunity to harvest the land, his merchants will never travel safely, nor would he be able to exploit mines, forests, or rivers in the region. Basically, while your super fortress is still standing, the game is not over for you, and this war brings almost nothing for the attacker, expect wasting his time and gold.

That's why castles were useful even for the small nobility, willing to protect their independence from their peers. Without enough forces to besiege that castle, and hold the land, and protect his own land, no other lord would dare attacking you, because if he did so, he would lose a lot of men and money just to take your land. Making him quite weaker indeed. Probably weak enough to become a prey for small neighbours willing to take the lion's share.

Modern video games do quite a good job to show it. I'm thinking of the Total War and Crusader Kings series. It is easily seen in game, that even a small enemy can be a tough nut to crack when he has a strong fortification. Of course, you can ignore his army and plunder his land. Of course, you can besiege it for years and lose men by hundreds before taking that tiny city. But if you ignore it, then one day his army will come out of the castle, and attack your own village. It will not defeat you, but if you are at war with someone else, you will lose a lot of time, and an important part of your economy. If you besiege it, you will lose a lot of time and perhaps a lot of men. You could even end up in another war, because your neighbours can see you lost troops and are now quite weaker.

In such games, without strong fortifications, the small country's army could just be crushed in an open ground battle, with much less losses, while grabbing the land easily.

That's the point of view of the tactician. Now on a much larger scale, if you don't limit your view to your own castle and to a small war, having such a stronghold is a big thorn in the toe for any invader. Your stronghold, if not taken care of, can:

  • Disturb supply lines
  • Disturb communications
  • Conduct guerilla warfare, while benefiting from an unassailable lair to rest and rearm
  • Secure some critical resources
  • Act as a strong bridgehead for any future counter attack
  • Secure the flanks of any allied army
  • Act as a supply depot for any allied army

And so on.

If taken care of by your enemy, then your stronghold still grants benefits in a campaign by :

  • Tying down enemy forces, much more forces than what's needed to protect your stronghold
  • Gaining time, because such forces will need an invasion force to plan what to do, to split up forces, organize a good siege before leaving. Or else, we're back to "Your stronghold is not taken care of" if the invader does not set a good besieging force.
  • Win the economic war. Your castle is a strong asset, it took years to build and cost a lot, but will last for tens of years. When the war breaks out, you most likely have to spend very few bucks on your castle. However, your enemy must still spend money for all these men besieging you. Each passing day, he loses money. Each day that passes, your castle is more and more profitable. In the middle ages, a professional force cost a lot to maintain, good weaponry is incredibly costly, especially for good steel, and these men aren't going to fight for free.
  • Decreasing efficiency of the enemy's chain of command. Your stronghold doesn't need many qualified men to hold its ground. Mere sergeants are enough to motivate the troops, even though qualified officer might help. However, besieging a fortress requires at least one or many experienced siege engineers and/or officers to know how to set up the forces, prepare for sorties, prepare their positions in case an external army come to break the siege and so on. In your case, your castle is already built, and it was built by the very same qualified people your enemy now needs to besiege it. You have these qualified people at your disposal to do whatever you want, while your enemy must leave irreplaceable assets behind.
  • Your strong castle might be one out of a strong network of castles, forcing your enemy to leave one castle at a time a small force to besiege it, weakening slowly its army. Should your own fortress be too weak, your enemy could storm it immediately. Here, having an impregnable castle is important.

I hope it will help you. Just remember though, do not fall for the classical Maginot trap : your stronghold will never be invincible, and an enemy might still want to avoid it, even though it means all the points we saw earlier. Thus you must take that into account, and perhaps even build your own strategy around it. A strong enough fortress might deter anyone to attack you, deflecting any invader to a less protected region.

That's what some modern days fortress were meant to be in Belgium, France, or even Switzerland, and some did their job well. Maybe that's what you truly need.


Impregnable fortresses/castles don't exist.

What a fortification is meant to do is delay the enemy, so that defenders can get their acts together/evacuate the civilians, before they are overrun. Historically, any group that has relied exclusively on walls and fortifications has lost, as their opponents, simply walked round the wall, e.g., the Great Wall of China or the Maginot Line.
You therefore need two things to have an effective fortification (or castle, in your case).

  1. The enemy must be willing to attack it, rather than avoid it. A reputation for being impregnable is a demerit.
  2. The capacity to last long enough for reinforcements to arrive, and hopefully, do some damage to the enemy in the meantime.

Ideally, your defensive structures should act as a funnel, controlling your attackers' mobility. You get to control how fast they can move, and what routes they take. Impregnability isn't needed.

  • $\begingroup$ "The enemy must be willing to attack it, rather than avoid it." -> The point of building a castle in a area is, more often than not, gain control over that area. If the enemy can choose to avoid the castle alltogether, chances are it is not strategically placed at all. You don't lay siege because "the castle has not an impregnable reputation", you do because you need to. $\endgroup$
    – Liquid
    Commented Aug 17, 2018 at 13:20
  • $\begingroup$ If one castle could cover all potential lines of attack, masons would be out of business. A castle is one structure as part of a series of fortifications. Unless built solely as a display of wealth, castles always come in sets $\endgroup$
    – nzaman
    Commented Aug 17, 2018 at 13:41
  • $\begingroup$ Surely, but that sentence kinda implies that a "impregnable" castle is somewhat not an optimal choice for the defenders. Of course the attackers are going to attack whichever, in their opinion, is the weakest avaible link in the chain, but this is a whole other matter entirely. $\endgroup$
    – Liquid
    Commented Aug 17, 2018 at 13:57
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    $\begingroup$ @Liquid: Precisely. The point of a castle is to stop the enemy in their tracks. If the enemies don't visit, it's only a white elephant. The only reason to have an allegedly "impregnable" castle, is to hide the inherent weaknesses of the location. Or to taunt an egomaniac enemy general. $\endgroup$
    – nzaman
    Commented Aug 17, 2018 at 14:06
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    $\begingroup$ The OP is using a word that has nothing to cling to except ideology. Masada was impregnable... until it wasn't; Fort Sumter was never taken, yet they still lost the war. The OP doesn't get to handwave reality if it's what they're asking for. (+1) $\endgroup$
    – Mazura
    Commented Aug 18, 2018 at 16:09

One does not simply build a castle

A complete castle is a formidable structure indeed, but its site was strategic before it was there.

The building of a castle is an organic process. It might begin with a simple campfire, then perhaps a wooden wall, a lookout tower, an armoury, a barracks, etc. Maybe there is a day when the wooden walls are replaced with stone walls.

The strength of a castle is dependant upon the strength of the attacks. If attacks are frequent enough, then the nobility will keep home there, and perhaps there will be a place to trade.

The castles that exist in present time exist simply because they were not in a strategic place during a modern war. They have become symbols of wealth and tourist destinations. Many have been built up bigger than they ever were while they were functional castles for those reasons alone.

  • $\begingroup$ You should explain, for those who do not know, why the nobility would choose to live somewhere which is attacked frequently. (They did so, of course, for the same reason that the robots in the Robot City series of books eventually would guard something by sitting it on a table before themselves rather than lock it in a more secure vault.) $\endgroup$ Commented Aug 19, 2018 at 6:00

Tidbits to add to the fray here:

Castles require a garrison. Indeed there is a fairly close ratio between the length of the outer wall and the number of men required to defend the walls. Clever use of natural features (lake, river, cliff) could reduce the wall to be defended.

Because they require a certain number of men per furlong of wall, castles were made as small as possible and still function. Not all were tiny, but the tradeoff between interior space and manpower requirements were carefully considered. There is some advantage to larger castles: Room inside goes up with the square of the diameter, while the amount of wall goes up only linearly. But you don't want a castle that requires every able bodied man for 2 days travel to man the walls.

Disease was a big thing in siege warfare for both sides. Let typhus run through the besieging army, and you could get a much weaker opponent without loosing a single arrow.


Your question is in two parts. First, why build a monster of a castle someplace it isn't strictly necessary, or strategically sound. Second, why would an enemy be bent on getting in when it may be easier to sit and watch you starve.

I think politics is a good answer to both. First, a castle isn't only a fortress, but a statement of intent, of power, and status. I do disagree that the garrison is more important than the brick and mortar. Suppose you are a warlord and have in your possession a very nice pile of gold. What to do with it if you aren't planning on going off to conquer more land? Invest in something very visible to tell your neighbors not to screw with you.

You build it because you can, because someone who could build a giant castle next to an unimportant but very pretty lake is someone who has power and status. The bigger the castle, the more materials used and the better maintained it is, the more others will know of your vast wealth and vigilant oversight - both being important factors when considering the strength and smarts of your opponent or rival. You make the castle strong because that's just being professional.

Alternately, the position of the castle is not strategically important, but culturally important. It is a symbol of power or tradition. Whoever holds it hold the honorary position as its steward and that grants political clout.

The second question is why would an enemy need to attack directly. That could be answered by what you have within your walls. In the game of warlord politics, power comes both in strength of arms and in legitimacy to rule. You (the attacker) may have the bigger army, but that stupid castle holds the family that has ruled this land for generations. Even if you pen them in, there's always a chance they could stir something up. They could escape and raise an army, or someone may try to assassinate you to put them back in their rightful place. Maybe your next target will get important time to prepare, or a neighbor is preparing to attack while you're busy picnicking in front of a foreign castle. No, a smart warlord breaks down that castle to end their rivals just as soon as they can so they can get on to other things in peace.

Winter is coming, too. You have the advantage now, but if the snows come early, your men will starve and freeze outside of that castle. You can assault it now, end the threat and have a nice warm home for the cold months, or you can pull back to your own encampment. In the mean time, though, the winds could change. Messages could get in and out of the castle. New allies for your enemy could appear, and you may not have the advantage again.

If the attacker isn't playing the plunder and pillage game, but politics with the intent to control the land and rid themselves of their rivals, a castle holding their rivals would present a huge obstacle and threat to their ambitions, as well as being their main target. Once military and political opposition is eliminated, they can do whatever they came here to do. There may need to be a ticking clock to encourage a storming of the castle rather than a siege. Other events occurring, movement of another rival's armies, etc., or even the weather changing could make an attack imperative. If the leader believed they could lose their advantage if action isn't taken now - and they need something in that castle ASAP - a storming may be in order.


There's a lot, like a LOT of good information here, so I'm going to try to cut straight to the heart of the question:

Question: Is there a good reason to build really tough castles unless their position is very strategic?

Answer: Yes. The primary reason would be to protect something that can project power REGARDLESS of where it is. There are all kinds of examples of this sort of thing. For example, a symbolic authority figure can have a HUGE impact just by staying inconveniently alive when other people would like to kill him so that they can usurp that authority. People like Nelson Mandela and Ghandi for example projected ENORMOUS power even when they were imprisoned in someone ELSE'S castles.

Less symbolic examples would be repositories of information that are not accessible anywhere else, or weapons with intercontinental (or interplanetary) ranges. Said weapons could run the gamut from nuclear weapons to information warfare tools that just require a satellite feed.

For that matter, you might need a strong fortification just because it's Not Safe to live anywhere else. In a sufficiently apocalyptic environment you might need a castle (or equivalent) to survive onslaughts of zombies, vampires, werewolves, or even sufficiently extreme weather.


Castles were often just mansions of medieval Europe.

But the point being, Why would you hole up in a castle? So someone could come and save you. As long as you're keeping your enemy at bay you can await reinforcements from friendly troops.

Of course time periods and definitions of castles effect the answer a lot. Many castles were quite small, basically being a status symbol and a place to hide if someone tries to kill you.

But the earlier definitions of castles are actually more like forts, towns with defensive perimeters to protect them from foreign invasion.

Larger castles belonging to Royalty were usually a status symbol passed down through the family, though it also had plenty of rooms inside to provide a variety of activities for the royals inside.

As far as a super strong fortification, I would recommend an enclosed city, where the wall is the main fortification, not the castle. There would be room for soldiers to defend, and if some amount of land was inside at least some food could be produced, hopefully waiting out a siege in a war of atrophy. Only the most important cities would need this though.

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    $\begingroup$ It is not correct that they were just mansions. Sure, some were (maybe even most), but not all. Castles placed at chokepoints are of significant military value. $\endgroup$ Commented Aug 17, 2018 at 9:05
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    $\begingroup$ That's true, there are castles built at strategic places; but the majority of castles were built to control the people within a country, either by showing political power or deterring uprisings from locals. $\endgroup$ Commented Aug 17, 2018 at 9:10
  • $\begingroup$ Mind you that I'm no history buff, but … IIRC, they often became mansions because the nongentle nobles would reside there. Eventually, when the need to command arms had lessened, and the noble was able to live with less military turmoil, the castle would become decadent. Of course, on the other hand, sometimes the castle was built simply because the lord and lady needed a place to live, and they needed it fortified and able to house their courtesans and garrison. Consider the non-fortified manors built to house the gentry in Victorian England. $\endgroup$ Commented Aug 19, 2018 at 6:13

Ancient and medieval warfare had none of the speed and mobility of today. Marching your army from your capital to the battlefield could take weeks or even months.

That means if you do not destroy the enemy, as soon as you leave he will regain control of the lands you just conquered and everything was for nothing. If the enemy retreated into a castle, you had no choice but to besiege or assault. Yes, you could leave him there and take control of his lands, but sooner or later you need to leave (home or to other battlefields).

Castles could and did tie up an enemy army for years. That means you cannot conquer someone else in that time, you need to supply and pay your army for that time, and very often you yourself had to be in the field and run your kingdom from a tent for that time. All of these things are a major nuisance.

The utility of a castle is not what you can or cannot do while in the castle. The utility is that it preserves the army and means if the enemy leaves without taking the castle, within a day or two everything will be back to what it was before he came and all his warfare was for nothing.


Some additional uses for a castle:

Keep your treasures in it

Every ruler has some things he really does not want to loose:

  • his gold and silver

  • his documents

  • his wife and more importantly, his heir

  • his court mage

  • his lover...

If the enemy could send a small raiding party and destroy or take these things while the ruler is busy fighting the main invasion force, it would be a great problem. He can fight bolder if he knows that his loved ones and most priced possessions are safely in a strong castle.

Weather invasions of nomadic horse-archers

Nomadic hordes can sweep punny feudal armies from the field. But they usually suck at besieging castles. Indeed, castles are so useful against them, that after the Mongolic invasion of 1241, King Béla the IV of Hungary started issue land grants on the condition that the recipient builds a stone castle on it.

Create a defensive area of hundred of kilometers depth

All the blue and black crosses on this map are castles built by 15th century kings of Hungary to defend against the Ottoman Empire. It took about a century for the most powerful land army of the word to get past it:

enter image description here

A single castle is good, but a in-depth defensive belt of many strategically placed ones is even better: Frontier pasas can not simply launch expeditions deep into Hungarian territory. The full mobile army of the Padisah has to come, but since it assembles deep in the south and marches long through the Balkan, the King has time to assemble a counter-force. And even if the Ottomans take some great castles, the defenders still can try and get them back after they have left, or simply build new fortifications before the next campaign season.

And remember, this was after the invention of firearms, and many of the castles were only wooden fortifications.


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