In a world where magic exists. A large army can hire several mages that able to cast spells as, or even more, powerful than a 16-19th century cannon. The city walls will not keep out a determined mage for more than a few days.

For example: On average, a mage can cast 4 large fireballs per day. 1 fireball is enough to make serious damage to the wall. So, an army with mages can easily break a wall but are not strong enough to raze it down.

Real-life research: In the middle ages, many cities required high walls to protect the people during sieges. The wealthier the city, the better and stronger the walls. When gunpowder and cannons using stone balls were introduced, walled cities soon lost they advantage and many started to decline. This gave rise to the "new" design of bastion or "star" forts which were better suited to outlast the destructive fire of the powerful cannons.

When the cannons switched from the 15th - 16th century stone to more effecive iron balls and shot during the 16th to the 19th century it sounded the deathblow to the effectiveness of high city walls. Only the wealthiest cities could afford to make all the changes necessary for effective defence against the advanced cannons and even then they were soon rendered obsolete.

It was during this period, the Middle Ages, that cannon became standardised, and more effective in both the anti-infantry and siege roles. After the Middle Ages most large cannon were abandoned in favour of greater numbers of lighter, more manoeuvreable pieces. In addition, new technologies and tactics were developed, making most defences obsolete; this led to the construction of bastion forts, specifically designed to withstand artillery bombardment though these too, along with Martello towers, would find themselves rendered obsolete when explosive and armour piercing rounds made even these types of fortifications vulnerable.

Limiting Factor on Magic System: Searching Medieval army sizes on History Discussion Forum, the first answer found stated that instead of the 100 000 - 500 000 (or more) soldiers often mentioned, modern scholars believe that armies were closer to 10 000 - 15 000 soldiers only. Coalitions being maybe double that at 30 000 soldiers. If an army this size could only retain the use of 6-7 mages, that indicates that magic is fairly restricted/expensive in the fantasy world in question (if we used the larger embellished numbers, magic users would be even rarer).

In a world with mages capable of destroying city walls in 2-3 days, why would people still find it useful to have these "old-fashioned" high walls around their cities?

Note: the question isn't focused on how powerful the mages or the fireballs are, but rather if and why the cities would still find high walls useful in the wake of such destructive forces.

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    $\begingroup$ Depends on what the magic does. $\endgroup$ Oct 22 '14 at 18:38
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    $\begingroup$ You're going to need to specify the nature and power of the magic $\endgroup$
    – Tim B
    Oct 22 '14 at 18:49
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    $\begingroup$ @vincent - is the assertion a fireball would do serious damage to a wall correct? In a traditional magic sense, fireballs don't do much to walls (it's more about the fire damage than any form of concussive impact, and a stone wall doesn't burn much). Am I off in saying I don't think fireballs would do much to a wall? $\endgroup$
    – Twelfth
    Oct 22 '14 at 20:05
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    $\begingroup$ @Vincent An explosion that has a solid surface at one side of it and completely open air on the other will waste the vast majority of its force. If I were to design a wall-breaker spell I'd come up with an impactor that drives partway into the stone before exploding so that the majority of the shock wave will go into the structure of the wall rather than into the air.. $\endgroup$
    – Shadur
    May 3 '17 at 15:01
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    $\begingroup$ Not enough for an answer, but if your mage's magic doesn't arc - i.e. they need direct line of sight, a wall can protect those inside from all forms of magical damage while it stands. $\endgroup$
    – bendl
    Apr 9 '18 at 19:56

20 Answers 20


Going to post an answer that contradicts one of your assertions on one simple premise:

Walls > fireballs

A fireball (using almost any definition of magical fireball I can find) is a ball of fire. There is no mass, just pure heat and flames. A wall is nearly immune to this.

A meteor swarm (probably one of the highest level spells any system has) would have the effect you are going for much more readily...to be effective against the wall, you need some form of mass to impact it or at very least concussive force, both of which a traditional fireball lacks in. Though if your armies contain mages that can through around meteor swarms, I'd suggest the concept of army is basically obsoleted by a few mages.

Goes back to the earlier "Enchanted Cannon" question...mages are great on soft targets, but unless extremely powerful there isn't much a standard 'evoker' style mage can do to a wall. When walls need to be knocked over, seige weapons are required, even in a medival magic prolific environment.

So answer = yes, walls are still exceedingly effective. If you are saying that a standard magic user can throw around massive concussive force fireballs that could tear holes through walls, then I'm back to suggesting you have some heavily powered up magic users that have little need for an army if they wanted world-wide dominance.


This question suffers a bit from the one-side problem I've seen more than once on here: You're surmising that the attacker has access to magic but the defender doesn't.

  • A large, solid and permanent structure that surrounds the entire area you want to protect sounds pretty much perfectly suited to anchor defensive wards of various types and flavors.

  • As mentioned above, a fireball does a lot of damage to squishy and/or flammable targets, but large thick stone walls aren't either of those (and historically, it tended to take way more than a couple of flaming arrows to ignite a wooden palisade wall) You'd be better advised to lob your fireballs over the wall and onto hopefully more flammable roofs and houses.

  • In fact, fireball spells tip the scales toward the defender much more than the attacker, because the main problem with using cannon defensively was that they were tricky to aim at anything smaller than the broad side of the proverbial barn, whereas a fireball spell is basically "you see it = you hit it" -- and if the siege mages can see the walls, any defending mages on the walls can see them. Hopefully they were not standing too close to the rest of the army divisions they were part of...

  • More generally, the purpose of a wall, as mentioned above, isn't so much to keep a sufficiently motivated enemy out indefinitely, it was to make it too costly in terms of time, manpower and resources to make it practical, in the hopes that an attacker would find someplace less well defended to bother.

Adding magic to the mix will likely change the nature of how walls are built and designed, but the idea of a solid barrier between "outside" and "inside" isn't going to become obsoleted quite that easily.


If magic isn't just used for offense, but can be used defensively as well, then walls could serve two purposes.

First, the walls themselves could be magically reinforced, countering offensive magic with defensive magic.

Secondly, a walled city would be more contained, thus being more amenable to casting various defensive emnchantments on the population than a sprawling unwalled city would be.


While armies love to have their cavalry and, in your case, their wizards, they win or lose on the backs of their infantry.

Your wizard is actually less combat effective than a cannon. 4 shots per day per wizard. And that wizard is probably more expensive to operate than a cannon, since she can charge exorbitant rates and probably demands better living conditions than anyone below officer rank in your army. For 4 shots a day, plus some lesser magical effects along the way. Meanwhile, your cannons can fire all day, as long as you have crews, powder, and shot. And yes, they require a crew, but that crew requires far less training than your wizard.

That's why the entire army isn't wizards with a handful of bodyguards. Infantry are cheap by comparison and effective.

So you need low-tech, easy to maintain, defenses to keep the infantry out. Yes, they cannot stand forever against the might of a wizard squad. But they can slow down the enemy long enough to mount an active defense via counter-attack.

This may be high walls, or it may be low, sunken walls like the bastion forts. That would depend in part on how long warfare and wizardry have worked together. If wizardry is relatively new to war, then you're going to have standard castle walls beginning to give way to bastions. Much as you see in history as gunpowder become more reliable and effective over time.

If wizards have always been combat-effective units in war, then there's a high probability that high-walled castles and cities never evolved at all. They simply wouldn't have necessarily been the best defense against the infantry/wizard combo. Maybe the engineers would've learned of the bastion style sooner. Or maybe they'd come up with something far different.

I would hazard a guess that you'd find some kinds of defensive spells imbued into your defensive construction, as well. Some kind of spells to make them more resistant to your wizard attacks as well as infantry. Much like you see an escalation over time as armor and arms try to out-do each other, you'd have wizard attacks and wizard defenses in a similar arms race.


You ALWAYS have to define and restrict your magic. If you don't, there's nothing a magician can't do, and the story falls apart at the seams.

So imagine magic only working on organic material, and being line of sight. The walls, quite apart from making control over who enters the city easier, now seriously hamper mages from harming people inside the city from the outside.

Or your mages can as you say cast only 4 spells that can damage a stone wall per day. Now you make those mages rare, so an attacking army can't muster more than a very few of them and will have to decide how to use them (attack those walls, or maybe do something else).

All depends on the boundaries and limitations you set on your magic.


Depends. Can mages also be paid by the besieged to counter the magic being cast against their walls? The walls were not designed to protect against a siege, they were designed to keep enemy armies at arms length from the town. Hopefully they'd move on and find a different town to sack or run out of money to keep the siege going.

So unless every band that could threaten the town has a few powerful mages to handle the walls, the walls would still serve a purpose. If you buttress the walls with a mage of your own to strengthen them from attack and to counter attacks, the walls will still keep out the average soldier/raider.

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    $\begingroup$ These answers should really be comments until we have a better question... $\endgroup$
    – James
    Oct 22 '14 at 20:30
  • $\begingroup$ @James He did add to it. But in my opinion, if you can use magic to tear down a wall, you can use magic to protect it. No matter what, mages in battle is always going to suck for those facing it without magic of their own. $\endgroup$
    – bowlturner
    Oct 22 '14 at 20:51

Walls generally both keep people out and people in - the higher the wall, the more effectively they do this.

Although a wall may not offer much resistance to a concerted attack, by either a mage or an army with heavy artillery, it will still offer some and will certainly withstand weaker forces.

Walls themselves, with limited gate access control the flow of most people in and out - this can help control infiltration by spies and defection by traitors, and undoubtedly would in a war situation.

A walled city also offers some level of protection to citizens who may normally live outside in times of peace where, otherwise, they could be easily picked off by any enemy soldier. Likewise their livestock, which in a siege situation might provide an important food resource.

Why would they not have walls?


The lock on my front door isn't going to stop a determined burglar from kicking in the door, but I still lock it because it stops casual burglars from just walking in.

Having high walls limits the kind of tactics your opponents can use. Cannons can be mass-produced; if mages cannot be mass-produced, having a big wall is advantageous because the opponent cannot attack unless they have mages. This means that the attacker would have to commit more time and resources to a carefully planned attack.

There is also the law-of-false-comfort: the government may maintain the large walls because they give the citizens a false sense of security, rather than because they serve any real strategic value.

  1. As someone already pointed out, if your invaders have to knock the wall down, you buy some time, regardless of how much. Time is essential to warfare... as Napoleon said, “Ask me for anything but time.” A lot can change on a battlefield in minutes, let alone days.
  2. Even the ruins of a wall are more defensible than an open urban area. They didn't call the first charge on a breached wall the “forlorn hope” for nothing, you know.
  3. Any numerically small group within an army is relatively vulnerable to both disaster and enemy action, so while wizards are useful, they're possibly, if not probably, not going to carry the battle alone, so any mundane defenses are still valid.

Let's for a moment accept your premise that mages will be able to breach your city walls within two or three days.

That still requires the attacking army to survive long enough while the defenders most likely will try to hinder their survival with any means they have available, including but not limited to magic.

Living for two more days already is an advantage in its own right. It allows you to do pretty much anything you damn well please, be it fighting back, or grabbing your valuables and escaping through that secret tunnel (or the back gate), negotiate, or anything else you might come up with.

And then there is the fact that it means your attacking army needs to hire those wizards first. Any army failing that will stand somewhat helplessly in front of your wall, looking up at heavy things being dropped on them.

So, I would say being attacked successfully by fewer armies is an advantage, too.

I'd definitely prefer having the wall in your setting than not having it.


First, one comment: The question sounds as if the magic from D and D is being used, rather than a magic system more useful for a book.

A lot will depend on the cost of magic, or rather the mages that cast combat spells. If they are expensive, this serves the defender who can offer a mage a comfortable living environment and good pay for little work only in defense. If the magic includes clairvoyance and other ways of information-gathering, then it will be difficult to sneak up on a city defended by mages.

One thing that I've seen few books address is that tactics would change if magic is a part of war. If fireballs are so useful against a stone wall (not that I think they would), then the walls would be built differently. They would be warded. Perhaps the very shape of the walls would be different to reflect the difference in combat.

Likewise, the concept of a siege might change. If there are ways for the defending mages to produce food and water for the people, a traditional siege might take too long for the attacker to use. It might come down to magical battles between the two groups of mages.

And, given powerful mages (why aren't they ruling the world already?), I would think the attacker would do better sneaking in a mage or two before he brings his army in. Then the attacking mage that is now inside can wreck havoc and let loose whatever he has. Or perhaps the attacker could buy/extort one of the defending mages with the same result.

Even worse than fireball would be some form of teleportation. I cringe at stories where the spell for teleporation is unlimited. I can think of so many ways to use this in combat that it would change everything.

  • $\begingroup$ +1 to "I cringe at stories where the spell for teleporation is unlimited." $\endgroup$
    – RonJohn
    Apr 9 '18 at 17:05

The thing is that this is like putting up a lock when you hear a master thief is on the loose. Will the lock stop him? Probably not. But will it slow him down? Maybe by a fraction of a second. The walls aren't there to STOP the invasion. They are there to slow it down. Besides, if you encounter such walls, you will need to hire a cannon force/wizard, which will take away war money for normal soldiers.(As an after thought, couldn't you get enchanters to reinforce the walls?) edit: I know there are some people saying the same thing but I posted this, then started reading the other ones. sorry


So many answers and I'll just add mine!

Premise: magic is powerful but time consuming, allowing wizards to destroy walls with spells.

Question: would walls still be used?

Yes, they definitely would. Considering the amount of wizards available for a trained army there will be a lot more "civilian" mages available, from the local witch who cures your pigs but is distrusted to a venerated member of the city. These mages would at it's core be about Food, shelter and Sex. The ability to get good food keeps you strong and alive. Sex contains everything from looking good and being able to convince others to have sex with you to protecting and nurturing your children, and shelter is anything from finding or creating a warm spot in a ditch to protecting your house against insects and fire breaking out.

Considering the power of each spell it wouldnt be unimagineable that defensive spells against other mages began development the moment mages began creating spells to tear down the local townhouse. The biggest question would be: Will there be enough mages to fortify the walls against magical attacks? If the amount of mages remains around 1 per 2500 people (using the 6 mages per 15.000 soldiers) then it might not be possible to get enough mages to permanently ward your walls, or the task requires immense amounts of money and time even when considering walls are expensive anyway. This would mean wards would be created for important sections and others left open.

This problem would mean a more Japanese type of fortifications build around "come on in if you think you are hard enough", rather than the "keep em out at all cost" of Europe. Walls would be build with in-build slopes leading to walls that are somewhat climbable, with fortifications and chokepoints higher up as well. If the wall is breached by magic the slope in front (now covered with debris) will make entering much harder and keep an advantage for the defenders, and the attackers would still need to breach the next fortification. It would also be easier to get out and mount counter-attacks to attempt to disrupt enemy castings, and potentially assassinate the mage(s) at a casting.

Lastly if protective wardings are impossible, then counter-mages might be used (probably used anyway). A likely section of wall is selected, mostly based on where attacker mages/their bodyguards seem to gather, and one of the few city mages is placed on a wall section nearby. This mage tries to disrupt the casting or kill the enemy mages, hopefully from a position that isnt going to collapse. Walls might become a series of low walls that area relatively easy to take so that it reduces the effect of a single breach on the outer walls and doesn't become too ludicrously expensive, giving the defenders the time to hold out and increasing the expenses of the attackers as they try to breach.


Without retreading too much ground posited by previous answers:

Any enemies that do not have access to mages, but have an abundance of line infantry, ie, mongols. Provides control over entry. Gives sense of security to citizens. Slows down any army that is a credible threat.

And finally my own contribution, disease and quarantine. If any sort of Bubonic style plague rolls through, high stone walls will be more than sufficient to stop hordes of potentially sick peasants from coming in.


If a mage can create a destructive impulse, then another mage can create a shield. This has been the history of warfare.

A defensive shield could take various forms: Could be a "structural integrity shield" that knits the whole wall into a single entity, so a mage's blow is dissipated over the entire structure.

It could be in the form of a mirror spell, the reflected the assaulting mage's blow back on himself.

Not all people are mages. So the walls keep some people out. Attackers have to bring up additional tools/resources.

Siege engines didn't stop cities from making walls. Siege engines were difficult and time consuming to move, and operation took effort. A siege engineer was a highly valued specialist. Meanwhile, while you were waiting, perhaps the besieging army camp would be thinned by an epidemic of cholera or typhus.

When cannons came in, it became both faster and cheaper to take out a stone wall.

As another analogy: We lock our houses. It keeps out the delivery man, and the neighbourhood kids. It doesn't keep out someone with a lock pick, bump key or sledgehammer.

A good magic system requires carefully design. If all things are possible, then you have to ask why any action isn't done with magic. There have to be both limits (not all things are possible) and there has to be a price (No free lunch)

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    $\begingroup$ If magic can be placed as enchantments or rune-clusters, then a larger wall also means more "writing space" to apply those protections on $\endgroup$ Feb 22 '19 at 14:04
  • $\begingroup$ There don’t have to be limits... but it constrains storytelling space when everyone’s wishes continuously come true. :-) $\endgroup$
    – SRM
    Dec 21 '19 at 16:41

Fireballs are pathetic weapons, especially so against walls.

High walls finally fell to artillery because they could apply direct kinetic energy which shatters brick, and causes the walls to collapse. So I would first suggest using a better spell against walls.

However, assuming you have some wall shattering spell, there are three options to keep high walls

  • The wall shattering magic is a recent development (matching artillery development) and thus the high walls are a relic of the past which have not been updated to modern star forts by those who can't afford it. Fortifications are extremely expensive, and cities that are not immediately threatened may well forgo upgrades for a long time.
  • There are counterspells to reinforce walls against those offensive spells, hindering any siege
  • The mages in the city get some kind of advantage due to having access to permanent spell circles on towers, or some other rather immobile magic structure, and can retaliate against any sieging mages that try to bring down the walls.

Without making additional assumptions (re. defensive magic etc.), some alternatives:

  1. Mages that powerful are likely to be in charge. ~They~ build (have built for them) the walls to keep non-mages from bothering ~their~ cities. Mages own the cities; they aren't going to be in the employ of some non-mage foot-slogger.

  2. Walls exist to allow for gates. The existence of gates as the only means of access to a town or city forces all traffic through a bottleneck - this allows for control, of people, of trade (taxing goods to generate revenue for the city). If you want gates, you have to have walls high enough to stop people climbing over them.

  3. Walls - of some kind - exist to separate the civilised from the wild. Keep your livestock behind a wall and the wolves won't eat them; keep your valuables behind a wall, and they are safe from itinerant thieves and beggars. They also foster in-group identity: "those within the wall" vs "outsiders".


Frame Challenge

The walls aren't for the wizards. They are for animals (and certain monsters if they exist).

Maybe the walls won't last long against an army with magical support. But that's not what they are there for. They are for the bears, cougars, or even the occasional moose. Or if they exist in your world, goblins and kobolds and owlbears.

The walls stop creatures with no access to magic or even advanced tactics and technology. They make sure that they can't see the tempting humans and food on the other side, and created a limited point of access.


Multiple reasons:

As others have said, the walls are useful against the infantry. However, there's another advantage to a sufficiently high wall: Gravity. The taller your wall the more energy it robs from whatever is being shot at the defenders and the more energy it adds to whatever the defenders are shooting back with.

Your fireball-casting wizard is going to have a very big problem with attacking--namely, that archers on the walls outrange his fireballs. The higher the walls the more of the bow's energy can be used on horizontal velocity and thus the bigger the area in which it can hit.

Assuming no air resistance for maximum range you aim up at a 45 degree angle and the arrow comes back down at a 45 degree angle. Lets pretend our wizard is a 1' x 1' x 6' figure standing 400 feet away--any arrow that hits the ground between 400' and 407' hits the wizard. Now lets try that at a closer range, dropping 1' for every 2' of travel. Now we hit him in the front from 400' to 412' and 412' 6" still clips him. Almost twice the distances that hit and thus twice the chance of the arrow hitting.


Come up with an in universe reason why magic doesn't work against high walls.

Why not go the other way? Maybe some long dead group of magicians created a spell that make high walls impregnable (so as to protect people). Since they're dead, and the spell is long ago forgotten, no one can undo it. "And believe me, we've tried!"

Even flying over them, if propelled by magic, is problematic. The walls detect any magic near it and cancels it out. That's part of the ancient spell.

So unless you're gonna pull a Kevin Costner (in Robin Hood) and catapult yourself over, its a no go. No Pegasus, no Dragons even, as they can be considered magical beasts.


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