The Fortress Builder's Toolkit

[Shining Wrath]

Imagine, if you will, that you are building a fortress in a D&D 3.5 world.

Definition: A "fortress" is an area designed to defend something or someone. It can be above or below ground, have walls or not, rely on physical barriers, magic, traps, and / or guards in any combination.

For example, you may be a Big Bad Evil Guy with a fortress lair. Or you may be the Treasurer of the Kingdom, building a fortress to keep the kingdom's crown jewels safe.

Assumption #1: To a level appropriate degree, you have access to Tier I spellcasters, and are completely aware of everything they are capable of doing. You also know about rogues, Use Magic Device, assassins, every race extant on the planet, Diplomacy, Intimidate, Bluff, et cetera, et cetera.

By "level appropriate degree" (hereafter l.a.d.) I mean that, e.g., the village sheriff at level 1 may have met a wizard once and knows the local cleric can do some stuff, while a level 20 BBEG will have numerous high level Tier I casters in his employ.

So, what will a good fortress designer do?

To a l.a.d.:

The fortress will be protected against flight. There will be roofs in places a "real world" fortress wouldn't bother. There will be more archers than a "real world" fortress might have. There might be catapult ammo designed to deal with flying creatures. Roofs will be designed to deter landing on them. Under no circumstances will it be possible to bypass a high level fortress by flying past most of it to the BBEG / treasure. Inside the fortress, roofs will usually be low enough that flight provides no advantage.
The fortress will be protected against spying. Thin layers of lead metal are placed on roofs, between courses of stone in the walls, and so on. Magical protections will be in place at higher levels. Illusions will be used at higher levels. There's not too much to be done about "Contact Other Plane" except to vary the defenses - move patrols around, change their composition, et cetera.
The fortress will be protected against teleportation and Gate. At higher levels this will extend into the astral and ethereal planes. There's not much point to a fortress if someone can just hop into the middle of it, take whatever is being protected, and vanish. At higher levels this extends to teleportation within the fortress; you can't climb over the wall, get into the fortress, and then teleport to the desired room.

Players may have to allow the DM a certain level of "Hogwarts rules" here; JK Rowling never really explained why it was that wizards couldn't teleport into Hogwarts, and the players may have to allow the DM to just decree that no, you can't do that.
There will be patrols. At higher levels, if the patrol is mundane (e.g., a bunch of giants), someone will be carrying an item with Antimagic Field cast upon it.
There will be protections against invisibility and illusion at higher level. Key choke points within the fortress are likely to have permanent anti-magic fields, which has the triple benefits of protecting the mooks, revealing invisible and illusion-covered creatures, and protecting the locks on the doors from Knock, Chime of Opening, etc.
Guards at the gate will have instructions that cover most Diplomacy / Bluff attempts. At higher levels, some of the guards may be deaf, or guards which speak disjoint languages so that you can't possibly persuade all of them at once.


Not every place the PCs need to go will be a fortress, and not every fortress will be well-designed in terms of all these aspects of fortress design. Dwarves might forget to protect against flight within their mines, or something like that.

However: some important encounters should involve well-designed fortresses which cover all the bases.

:smallredface:Did I miss any important aspects of fortress design?
:smallcool:I've seen people say that anything a party can do, a Tier I caster can solo. Is that still true within a well-designed fortress?

EDIT:
The walls need to be protected against passwall in some fashion - again, no point in having a fortress that anyone can bust through. Supplement the thin layer of lead with a layer of iron. Make them bust down the iron and attract the patrol.

[Hamste]

The deaf guard suggestion is pretty bad, you want guards that can make listen checks.

The Anti-magic field thing is also a problem. If it isn't hand waved away most spells like forbiddance that stop teleporting don't work in Anti-magic fields. This means that it is possible to teleport into a patrol (You can't teleport in an anti-magic field but you can teleport into one) and use that as a vantage point to start the invasion. It needn't even be that big of an invasion, just enough to kill the mundanes and to make a small hole in the lead lining in a few random rooms. Speaking of holes, make sure that you have a low level scrying spell cast in the castle every so often to check to make sure that it is still protected (the lead of course works both ways)

You might also want to look into the cleric spells (and possibly wizards) that are particularly useful for defence, like create food and water, buffs (persistable, mass or long lasting are all good), wall spells and things forbiddance so that the DM knows what type of spells that their clerics should have prepared in case of a fight.

Underground fortresses also tend to be better than above ground. Not only are they harder to assault but they also hold some spell advantages. For one thing you no long have to worry about fliers or incredibly far ranged acid arrows. The natural risk for underground areas is meld with stone, however with a lining of lead they can't get in as easy. Keep in mind that the stone blocks your line of effect which is good for the defender. The main reason they weren't common in real life was the amount of time it costs and how hard it is to supply. With D&D magic it would be easier to keep it supplied and create it quickly. The main disadvantage is trying to hold off passwall. It would get to the lead wall and then just smack it until it breaks. It might be hard to counter this (Wall of iron is always good).

[Shining Wrath]

The deaf guard suggestion is pretty bad, you want guards that can make listen checks.

The Anti-magic field thing is also a problem. If it isn't hand waved away most spells like forbiddance that stop teleporting don't work in Anti-magic fields. This means that it is possible to teleport into a patrol (You can't teleport in an anti-magic field but you can teleport into one) and use that as a vantage point to start the invasion. It needn't even be that big of an invasion, just enough to kill the mundanes and to make a small hole in the lead lining in a few random rooms. Speaking of holes, make sure that you have a low level scrying spell cast in the castle every so often to check to make sure that it is still protected (the lead of course works both ways)

You might also want to look into the cleric spells (and possibly wizards) that are particularly useful for defence, like create food and water, buffs (persistable, mass or long lasting are all good), wall spells and things forbiddance so that the DM knows what type of spells that their clerics should have prepared in case of a fight.

Underground fortresses also tend to be better than above ground. Not only are they harder to assault but they also hold some spell advantages. For one thing you no long have to worry about fliers or incredibly far ranged acid arrows. The natural risk for underground areas is meld with stone, however with a lining of lead they can't get in as easy. Keep in mind that the stone blocks your line of effect which is good for the defender. The main reason they weren't common in real life was the amount of time it costs and how hard it is to supply. With D&D magic it would be easier to keep it supplied and create it quickly. The main disadvantage is trying to hold off passwall. It would get to the lead wall and then just smack it until it breaks. It might be hard to counter this (Wall of iron is always good).

Teleporting into the anti-magic field would be possible; but then your party is incapable of casting, the fighters are using mundane weapons, and thus a lot of the advantages of a typical party are taken away. Your visit to the fortress begins with a pitched battle with people who might well be trained to recognize and kill the casters. For example, imagine a battle within an AMF between an ogre and 5 gnolls versus a 4 person level 10 party (Warblade, Factotum, Wizard, Cleric). And the guards ignore the Warblade at first and go after the others. Will they win? No. Will they hurt some people? Probably yes - they get 6 actions per round, and someone is going to be able to reach the wizard who is standing there with no AC worth speaking of. And a large ruckus ensues, and the reinforcements / patrols are going to be there within a few rounds.

If the wizard tries to solo the dungeon, he dies. Dimension Door doesn't work, so our foolish wizard gets hit 3 or 4 times in the first round, has to physically run to where he can cast generating AoO, and then still can't cast into the AMF or summon anything. Not so good for someone with 4 + 9*2.5 + perhaps con modifier of 2 = 46.5 HP. If the gnolls have ranged weapons they can stay within the AMF.

[Emperor Tippy]

No, you build your entire base out of Aleax Ice Assassin Factotum 11/ Psion 20's that have been true mind switched with blocks of granite (or other building materials) and then stuck together with Sovereign Glue.

Yes, every single stone in the floor, wall, and ceiling. Every door, every window, every chair, every light fixture. They are all utterly loyal, utterly indestructible, level 20 Psions that have unlimited PP, all arcane and divine spells as powers known, get to act multiple times per turn, have spot and listen checks higher than god, and get to ignore PR/SR. Oh yes, and they all have permanent telepathic bonds with you.

Oh yes, and don't forget the Permanent Emanation Selective Planar Bubble's that they all have set to dead magic, time locked, demi planes that exclude the Lich (so he is the only one who isn't time locked and can use magic).

Well those are what you should be using as building blocks.

[Shining Wrath]

Well those are what you should be using as building blocks.

In the context of l.a.d., I'd call that appropriate for level +YES.

Also, I don't think I want to be in continual telepathic bond with several hundred (or thousand) psions who are BORED OUT OF THEIR FREAKIN' MINDS because they are, you know, blocks of granite. The view never changes when you're that stoned. What sort of games might a psychotically bored psion play with the only mind available to them, which happens to be mine?

[Threadnaught]

If the wizard tries to solo the dungeon, he dies. Dimension Door doesn't work, so our foolish wizard gets hit 3 or 4 times in the first round, has to physically run to where he can cast generating AoO, and then still can't cast into the AMF or summon anything. Not so good for someone with 4 + 9*2.5 + perhaps con modifier of 2 = 46.5 HP. If the gnolls have ranged weapons they can stay within the AMF.

Tippy's assault team managed to breach my fortress (read the spoiler) and I laugh at yours.

A massive hollowed out stone the size of southern Manhattan (including the skyscrapers) in space. Every single wall/floor/ceiling is Obdurium, or if not available Adamantine. Teleportation Circle docks at specific locations accessed via specialized gateways, gates are Portcullises made of the same material as the walls. All walls/floors/ceilings and gateways are augmented with Walls of Force. The streets of this city are all 10' wide corridors lined with a network of resetting Dimensional Lock Traps. An army of Shadesteel Golems on a constant patrol cycle to set off these traps in the streets and any buildings/rooms. On the Ethereal Plane, there are 27 Wierdstones spaced out evenly in a cube, along with more Shadesteel patrols in a more tight knit area around each of the stones. With just Obdurium/Adamantine strength stone filling the Walls of Force.

Tippy got in. Without even trying, though he did mention something that was blocked.


I laugh at yours because it can be teleported into and Instantaneous Conjurations are a thing. Also Disjunction = 1% chance per CL to destroy an AMF, which allows for Instantanious Conjurations inside your fortress.

[Shining Wrath]

Tippy's assault team managed to breach my fortress (read the spoiler) and I laugh at yours.

A massive hollowed out stone the size of southern Manhattan (including the skyscrapers) in space. Every single wall/floor/ceiling is Obdurium, or if not available Adamantine. Teleportation Circle docks at specific locations accessed via specialized gateways, gates are Portcullises made of the same material as the walls. All walls/floors/ceilings and gateways are augmented with Walls of Force. The streets of this city are all 10' wide corridors lined with a network of resetting Dimensional Lock Traps. An army of Shadesteel Golems on a constant patrol cycle to set off these traps in the streets and any buildings/rooms. On the Ethereal Plane, there are 27 Wierdstones spaced out evenly in a cube, along with more Shadesteel patrols in a more tight knit area around each of the stones. With just Obdurium/Adamantine strength stone filling the Walls of Force.

Tippy got in. Without even trying, though he did mention something that was blocked.


I laugh at yours because it can be teleported into and Instantaneous Conjurations are a thing. Also Disjunction = 1% chance per CL to destroy an AMF, which allows for Instantanious Conjurations inside your fortress.

I'm not trying to design The One True Fortress, I'm trying to design principles that scale up from level 1 to EPIC. The higher you get, the more stuff you add.

Like surrounding the AMF locations with a Force Cage which requires someone on the outside to lower it (obviously, inside the AMF you aren't casting anything at the cage). And archers. Many high-level ones. With poisoned arrows. Teleport into that as much as you like.

[Vortenger]

Guys, all due respect, but I don't think jumping in to the deep end of the optimization pool is quite what the OP had in mind. (Though I'd expect nothing less from the Emperor...)

For the average DnD game, your building blocks look fine. You are indeed going to want to come up with something aside from just AMF to prevent people from coming in by late game. There are several other threads dedicated to this very idea. I'm too lazy to link any right now, but you'll find 'em with a bit of google-fu.