Friday, 6 September 2013

I Capture the Castle (By Magic)

15jh castle siege

So Shannon has just written an article about traps and fortifications for her WOD-mechanised Fianyarr setting over at ST Wild, and these are things that I have spent a little time on myself. Well, traps I’ve already written more or less to death (at least in the absence of any brain-inspiring conversations), but fortifications have remained on my to-write list ever since a conversation with Dan about a year ago. Time to get cracking.

The story Dan mentioned was, I reckon, a fairly common one – a party of moderate-level D&D characters assaulting a castle by using transmute rock to mud to break through the walls. I’m not sure, at this point, whether it was the classic small party of heroes making a tactical incursion into the castle, or whether they brought an army of some size along with them, but it’s not too important. This is a very sensible tactic for a magic-wielding party to use to avoid a pitched battle with entrenched defenders using expensive fortifications to their advantage.

The problem I have is that it allows a magic-wielding party to avoid a pitched battle with entrenched defenders using expensive fortifications to their advantage.

This is not a GM issue for me, but rather a setting one. Most versions of D&D and similar fantasy genres assume a reasonable amount of magic – the wealthy have magical items and sometimes wizards on retainer, skilled warriors tend to have magical swords, and so on. Often the use of magic in wars is explicitly mentioned – there are a few fantasy books where wizards steer clear of mundane conflict, but these tend to have an otherworldly kind of wizard that doesn’t really lend itself to RPGs. So I think it’s safe to say that if you’re a landowner or warlord considering castle-building options, you can assume that at the very least the kind of people likely to want to conquer you will have access to serious magic, and very likely that far less well-resourced adversaries will have magical capabilities.

Castles are not cheap. A mediaeval castle could easily cost a third of a king’s annual income. Rochester Castle apparently cost £3000 pounds, while William the Conqueror had about £10,000 per year to spend, and a skilled labourer earned 2p per day. That’s 360,000 times the labourer’s earnings.

In AD&D terms, the labourer’s 2p is probably equivalent to a 1sp Sapper/Miner, which makes a castle around 36,000 gp – however, the rules give 500,000 for a Castle, so there are a few economic differences.

So anyway, you have your 100,000gp fortress, equipped with all manner of defences, expensive veteran soldiers and so on and so forth. And here’s a wizard with a 5th-level spell, which as a minimum can obliterate a 180’ stretch of your wall within a minute or so from 100 yards away. You still have to deal with some of the guards, of course, but you can bypass the main defences, take the castle by surprise, and very likely kill or incapacite many of the guards in the process of spellcasting. On a simpler level, a reasonably enterprising thief could obtain scrolls of passwall, or simply charm person, for a minimal cost compared to the takings to be had.

There's no specific cost given in the AD&D rulebooks, but even the most expensive equivalents would put a hired caster at no more than 10,000gp, which will render the fortress virtually useless for one-tenth the price of building it. In 3.5, it would be a mere 6,600gp while the Castle would be around 500,000gp! Who could resist?

The spell itself transmutes a 20’ cube per level of the caster, and walls may well be higher than this; but removing the bottom 20’ of a wall tends to rather disturb the higher portion. The spell is equally effective on towers of any height; in fact, the higher the tower, the more damage you can cause by toppling it. This is even assuming the castle is not – as they usually are – built on a rocky pinnacle, in which case you could transmute the rock itself without even approaching the castle, and quite possibly demolish the whole thing in perfect safety.

This is just one example of the power of magic against fortifications: passwall is another obvious example, while fly or invisibility allow individuals to bypass defences and wreak havoc. Even simple charm and sleep spells can eliminate guards near-instantly or turn them traitor (and it’s a fantastic defence for anyone thinking of actually committing treachery). Generally speaking, people do not spend vast fortunes on military projects that they expect to be completely ineffectual against inexpensive and relatively safe attacks; we don’t build stone castles or wear plate mail any more. Military practice changes to accomodate the available technology. In other words, in a setting where magic is prevalent, it makes no sense for expensive, long-term slow-to-build military-level fortifications to be unprotected against magical assault. Either they would be magically hardened, or else they would simply not be built.

In fact, if magic is fairly widespread, I would even suggest it’s more likely that fortifications would be physically primitive but magically warded, than that they’d be reinforced stone with no magical protection – that’d be the equivalent of forgetting to put a door on your castle.

In the rest of this article, I'm going to rely mostly on examples from various editions of D&D, as I don't want to try and find examples from systems I don't actually understand, and also out of laziness. A fair amount of the points in this article could be applied more broadly, to issues like law enforcement and border control, but I'm not going to go into those here.

Magical threats

Magic poses a number of threats to the typical mediaeval castle, which I’ll vaguely group for simplicity. Some are extensions of existing strategies, some parallel more modern developments, and some are completely novel.

Before I get into specifics... part of the effectiveness of magical siegebreaking is that spells often allow the caster to act at significant range, allowing them to lurk in nearby undergrowth, hide within a regiment, or even wreak havoc from the other side of a river without exposing themselves to attack. This is exacerbated by the benefits of other protective spells. For example, a wizard can use invisibility to approach a fortress unseen, backed up with stoneskin in case they somehow get spotted; they then have very little to fear in wandering right up to the fortress to demolish a wall or conjure up a demonic horde.

In general, wizards combine a number of different powerful abilities. Flight alone would not enable a fighter to conquer a castle, invisibility keeps you safe but doesn't accomplish anything, and fireballs can't easily bring down a castle to get at the chewy centre. The combination, however, is devastating.


I’ll start with this because it’s the example that inspired this article. There are an array of spells that allow a spellcaster (or anyone with suitable magical items) to wreak havoc on a fortification, often with minimal personal risk. I’ve already mentioned transmute rock to mud, which is probably the best bet in terms of result and casting level. Disintegrate is far less powerful, but can overcome even magical protections. These roughly parallel real-life demolition equipment.

Moving away from real-life options, control weather can potentially lay waste to large fortified areas, and at least can severely batter the inhabitants and damage structures. Earthquake is devastating, but very high-level. Move earth can render ditches and moats worthless without a single casualty. Even plant growth can potentially cause serious problems.


Force is one thing, but often your objectives can be through subtle means, most of which have no real-life parallel. If you’re interested in removing a perceived threat, or forcing a fortress to surrender rather than actually killing people, then assassination may be a better bet. Magic can easily allow you to enter a fortress without detection. The classic is invisibility, though that has a few loopholes – guard dogs, for example, with their keen sense of smell. Various forms of transmutation, from polymorph to being a druid, allow you to take on shapes that won’t arouse suspicion, be it impersonating a member of the guard or becoming a raven. You could turn into smoke and pass through keyholes to your target’s bedroom, or become an ooze to slide quietly through an arrow slit. Earth elementals can swim through solid rock.

As well as direct methods, infiltrators can potentially steal or copy keys, sabotage artillery, spill acid in armouries, poison or drug food and wells, spread magical disease, or even weaken walls from the inside (perhaps from a location that’s hard to access without magic, or rarely visited). Any of these would make a later attack much more effective.

The disguise-based options rely to some extent on the same techniques as real-life infiltration, and some mundane precautions may render them ineffective. Thus, key locations within a castle are likely to demand passwords (changed regularly), magically screen visitors, check fingerprints, or otherwise test identities. Such locations may include treasuries, armouries, prisons, stores (poisoning food and wells are well-known strategies), the quarters of important residents, libraries (important in a magical setting) and temples.


Of course, attacking or laying waste to a castle isn’t always the best bet. Maybe you want it yourself? Maybe you just don’t like violence. There are various spells which offer peaceful solutions to siege warfare.

Our old favourite is sleep, which has quite limited effect but can easily take out a crucial nest of guards, allowing you to nip up a ladder or (if you time it right) slip through the gate they didn’t have time to close. Charm spells can last for weeks, and a canny caster could waylay castle residents one at a type, charming a few per day to ensure their decisive strike goes completely unchallenged. More directly, a simple stinking cloud, fear, web or hypnotic pattern can render significant numbers of guards useless and are easy to cast. In fact, well-timed use of a single hypnotic pattern (24 hit dice of creatures) could well disable an entire garrison.

My (limited) research into castles suggests that standing garrisons in “classic” castles really were much smaller than typically portrayed; castles on the rebellious Welsh borders typically had up to forty men, and often far less, down to just a handful when the lord was absent. Smaller garrisons are cheaper, and require less food in a siege, so you want the smallest garrison that can reasonably hold a place. During wartime, with levies or reinforcements, somewhere from 60-150 seems to have been more common, with occasional surges where part of a nearby army joined the defenders temporarily. Later soft-sided castles, built with sloping banks of earth against the walls to survive artillery fire, were easier to attack and required larger garrisons. It’s hard to say what’s more appropriate for a typical pre-gunpowder fantasy setting with its array of magical and supernatural ‘weaponry’.


Knowledge is power, and in tactical terms, knowing the strength and nature of your enemy is a good start to defeating them. Magic allows an attacker to scout out all kinds of useful information about a fortification, depending on the time available. On a basic level, anything from scrying to familiars to fly or an invisible scouting run allows you to examine the layout of a castle, the defences it mounts at various strategic points like gates and towers, and the strength of the garrison –without alerting the enemy and giving them time to prepare. These are useful both for planning an invasion and for directing ordnance.

With more time to prepare, you can gather even more information. Scryers or hidden scouts can observe training, defensive drills and the quality of the garrison. The habits of important individuals can be determined, and which parts of the castle are rarely used or attract little attention. Guard routines can be recorded, and stealth attacks planned for those times where the most lacklustre guards will be on watch. And of course, you can find out how practical it is to attack the castle at all – if they have a lot of supplies it may be best to go elsewhere, leave a small guarding force to trap them and move on, or try one of the infiltration tactics.


There are a number of ways for magical attackers to simply bypass a castle’s defences, leaving them fighting perhaps a couple of dozen soldiers. These can be devastatingly effective.

To begin with, one person who gets inside can allow in large numbers by various methods. The wizard might use invisibility, flight, disguise self or charm to get inside, or simply pose as a harmless visitor (or ally) until their treachery begins. The oldest trick in the book is opening a side door, though a decent wizard can likely also seize control of the main gate if they wish. However, the defenders have a chance to spot the attackers as they approach the castle, as it’s very difficult to bring up an army (or even a sizable strike force) stealthily. Far more dangerously, a conjurer doesn’t even need a nearby army, but can unleash all manner of hideous creatures on the guards. In AD&D, a 5th-level wizard can summon 2d4 monsters to overwhelm guards or create a distraction. Later editions are far more generous: even an Int 10 5th-level D&D 3.5 wizard can summon at least six monsters (if they go for the highest available level), or as many as 1d4+2d3+4 creatures of minimal level., including things like swarms that have unlimited durations and are a big threat to low-level creatures.

Next, there are the actual bypass spells. I already mentioned transmute rock to mud, which can be used in a more subtle way to do this; but spells like passwall and phase door are literally designed for this, won't raise the alarm, and won't cause unwanted damage to the castle you're conquering. Particularly useful for things like the Great Wall of China, where you have no real interest in possessing the fortification and simply want to get past it.

Finally, you can simply teleport inside. This is actually less useful than passwall unless you know how to reach a really vital part of the castle, since your carrying capacity is usually quite limited, while a wall-passing spell can let hundreds of soldiers through.


This is such a massive divergence from mediaeval reality that I think it does deserve a bit of special attention.

We still don't have personal flight capability in the modern world, but we have had observation balloons, air recon corps, parachutists, helicopters, and of course a ton of aerial bombardment. Each of these made a big difference to tactics (though I don't pretend to be an expert on military history). Flying observation platforms provided long-range information on troop movements and dispositions in relative safety. Parachutes and helicopter drops allowed troops to appear behind enemy lines, avoid kill-zones and minefields, go right to strategic objectives without fighting through enemy troops, and reinforce or resupply ongoing battles (including sieges, of course). Bombardment allowed the flying side to disrupt or devastate the enemy in relative safety, since they're out of reach of many weapons - and missiles are the ultimate expression of this.

Now imagine how this would go down in a fantasy setting.

One major point is that fantasy tends to have very few long-range weapons, and virtually none suited to direct fire. Bows are all very well for horizontal fighting, but badly-suited to shooting targets far overhead.

Secondly, wizards tend to combine flight with the most devastating and long-ranged attacks in the game. A D&D wizard may be able to fly, while also casting fireballs from hundreds of feet above - many times the effective range of even a longbow. At the crudest, a 5th-level wizard can fly for five minutes, hovering just outside longbow range and blasting the defenders with infallible magic missiles that can easily slay an ordinary soldier. If they wish, preparing only fly and several magic missiles each day, they could wipe out a typical castle single-handed by doing this for a week. If they have any concern at all about getting hurt, a simple invisibility will solve that problem.

But a third and major point is that fantasy has a ton of creatures (even aside from wizards) that, unlike non-extinct real-life ones, combine two or more of these features:

  • Capable of flight
  • Intelligent
  • Reliably capable of killing a human

This is to say nothing of the devastating fantastical abilities of many creatures, such as hypnotism, breathing fire, acidic blood, invisibility and so on, which are qualitatively different from what (say) a lion can pull off.

Dragons are the most obvious example - there's basically no point building a fortress to protect what's inside from a dragon, if you have an open courtyard. But even ordinary towns might have looked rather different if they not only had to worry about wolves getting at the livestock, but also griffons, so a simple fence around the town would not have sufficed. If sieges regularly featured summoned stirges, celestial eagles or mephits swooping down on the defenders and slipping into the castle itself, people would begin to think about ways to keep them out. Even more so if invaders are liable to turn up on pegasi or wyverns.

Just in passing, let's also note that fantasy settings may also feature creatures that can burrow effortlessly through earth or solid rock, water elementals that can readily travel through normal water, and things that can just plain old walk through walls.


Another aspect of magic, which is probably easy to overlook, is the psychological effect. Psychology has always been important to sieges, from pretences at abandoning the siege, to catapulting mutilated bodies inside, to delivering fake letters authorising the defenders to surrender.

The subtle or dangerous effects of magic could be extremely influential on people's mindset. Given the potential for death from above, any speck in the sky might cause guards to panic in case a wizard is coming to incinerate them. The capability of a single individual to conjure up armies or obliterate whole swathes of guards seems likely to provoke concern pretty much on the level of modern anti-terrorism measures. But illusion and enchantment magic are even scarier. Not only is there the usual possibility of an imposter or traitor, but even someone who you definitely know to be absolutely loyal can be controlled with a snap of a wizard's fingers, forced to stand idly by, open gates, reveal passwords, or even attack their lifelong friends. Consider the damage those ideas could wreak on the mind once the possibility was suggested, and the ensuing paranoia. You wouldn't even necessarily have to actually do any magic. A whisper of wizardry might be enough to completely destroy morale.

This is really long now, so I'll save discussion of what castle-builders might do for another time.

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