[HR} Using Magic in Construction

This is the first time I have found myself with a question after reading the core rules, gone to the forums, and found out Alex has not already answered it.

It was weird. So I derived my own answer, using this thread (http://autarch.co/forums/ask-autarchs/constructionlabor-costs) plus the books as my starting points.

The question I’m attempting to answer is; how much can a high-level wizard help in constructing buildings, strongholds, and the like, and what should the rules for that be?

I found it to be an extremely difficult task at first because the book does not split between materials and labor. Then I realized; what if you just aren’t paying for materials?

That is, your labor costs include the cost of your men quarrying stone and harvesting lumber, then dragging those materials to the site, then building out of them. Under this assumption, having N GP worth of materials at the site simply reduces your construction cost (and time) by N GP. I use that as my core assumption for all of the following. Now on to the actual house rules!

General rules: In no case can the cost of a structure be reduced by more than 50% by magic, unless the magic being used can replicate the entire structure. For example, the cost of a wooden palisade can be reduced by 100% with a Wall of Wood spell, because a Wall of Wood is capable of creating a wooden palisade. Similarly, a castle wall can have its cost reduced by 100% by repeated castings of Wall of Stone. However, a tower cannot have its cost reduced by more than 50% by castings of Wall of Stone, no matter how many times you cast it, because the Wall of Stone spell cannot create wooden doors, floors, stairs, furnishings, and the like.

A spellcaster who is assisting in construction must work closely with the artisans and engineers. The necessary castings will be spaced out over the course of construction; thus a wizard assisting in the building of a small tower (5 walls of stone being cast over 28 days, the derivation of which will be shown later) would have to cast Wall of Stone the first day of construction and every five days thereafter. The spellcaster can do other things during the days they are not spellcasting, but must be available to the artisans for at least occasional consultation at all times during the process.

In any case where sufficient castings are required (Judge’s discretion how many castings is sufficient; my gut ruling would probably be 5 as a default, but you could go with as few as 2), one engineer per 100,000 GP base price is required. If a qualified engineer is not hired, the structure will be unstable. Whether it collapses on its own or waits for a stimulus (earthquake, catapult, gust of wind, light tap, whatever) is left up to the Judge, but the summary is that if you want it to stay standing for more than a week or two, you should really consult an engineer. (Note that an engineer hired to work on a project of this nature will charge you for the full month even if you complete the construction in less than one month.)

A Wall of Stone spell reduces the cost of the structure by .25 GP per cubic foot (250 gp per casting, to a maximum of the structure’s actual cubic footage of stone). This number was derived from the cost for 20’ and 30’ high curtain walls, both of which cost .25 GP per cubic foot.

A Wall of Wood spell reduces the cost of the structure by 1.5 GP per cubic foot (150 GP per casting, to a maximum of the structure’s actual cubic footage of wood). This number was derived from the cost for a wooden palisade, which costs 1.5 GP per cubic foot.

A Move Earth spell can be used both for excavating and for earthen constructions. When used for excavation, it reduces the cost by .02 GP per cubic foot excavated (derived from the cost for pits and moats). When used for construction, it reduces the cost by .167 (I haven’t decided where exactly to round that yet) GP per cubic foot, derived from the cost for an earthen rampart.

Transmute Rock to Mud (or vice versa) allows you to move mud around and build with mud, then turn it into stone. This allows you to build stone structures using the cost for an earthen rampart, which saves you .083 GP per cubic foot. (The total savings for a 20’ high 100’ long 10’ thick stone wall would be 1660 GP, requiring only a single casting of the appropriate Transmute. Note that a transmuted structure cannot replace the entire structure, as you cannot simply stack up mud 20’ high, and thus must obey the maximum 50% reduction limit, if somehow that manages to come up.)


A 20’ diameter, 30’ high stone tower (small stone tower) has a cubic footage of stone of (pi10030)-(pi56.2530) = 4123.etc. (Volume of the outer cylinder minus volume of the inner cylinder, with a 5’ thick wall, gives us radii of 10’ for the outer and 7.5 feet for the inner.) This will require 5 castings of wall of stone to create all of the stone necessary for the form of the tower. However, there are only 4123 cubic feet of stone to replace, so instead of the full potential 1250 gp for 5 castings, the cost of the tower is reduced by 1030 gp, from 15,000 to 13,970. It will reduce the required construction time from 30 days to 28 days.

Note: Original math is for a tower with a 20’ outer diameter, which is a little ridiculous. With a 20’ inner diameter, the outer diameter is 30’ (5’ of wall on each side), giving us radii of 15’ and 10’. This gives us 11, 780 cubic feet of stone in the tower; 12 casts of wall of stone will reduce the cost by 2,945 GP. Reducing the cost by 2,945 GP will reduce the construction time from 30 days to 25 days.

A generic stone building (20’ high, 30’ square, 1’ thick walls) has 2400 cubic feet of stone (20 * 120 * 1). This will require 3 castings of wall of stone to fully replace, which will reduce the cost of the building by 600 GP, from 3,000 to 2,400 GP. The total construction time will be reduced from 6 days to 5 days.

A generic wooden building (20’ high, 30’ square, 1" thick walls) has 200 cubic feet of wood. This will require 2 castings of wall of wood to fully replace, which will reduce the cost of the building by 300 GP, from 1,500 to 1,200 GP. The total construction time will not change, as the price was reduced by less than 500 GP.

A stone castle wall (60’ high, 100’ long, 10’ thick) has 60,000 cubic feet of stone. Sixty castings of wall of stone can create this entire wall out of nothing, reducing the price to 0. A 9th level wizard who can cast only one wall of stone per day would take 60 days to construct this wall, which is actually slower than the normal construction time of 45 days. (If the wizard wants to just cast wall of stone as fast as he can while the workers also work on it at a rate of 500 gp/day, at a rate of one wall of stone per day, the wall will be done in 26 days at a cost of 13,000 GP. I rounded a little to solve that.)

A wooden longhouse (15’ high, 30’ long, 15’ wide, 1" thick walls) has 562.5 cubic feet of wood. Six castings of wall of wood will replace all of this. The cubic footage reduction mathematically would reduce the cost by 843.75 GP; however, this is more than 50% of the cost of the structure, and the entire structure cannot be created out of walls of wood. Therefore, six castings reduces the cost of the structure by 150 GP, or 25 GP per casting.

The summary of these derivations is that it is really not worth the effort to hire wizards to build your stronghold for you; you get a bit of a time break but mostly it’s not a huge one. I’m happy about that, because if it were economically feasible to hire wizards to build strongholds, then more people would do it. Since it is economically infeasible, that means that this allows wizards to use magic to ease the burden on their own finances if they are willing to spend their own time, but non-wizards don’t feel that they need to hire one or more wizards to cast wall of stone all day.

I’m surprised by how effective Transmute Rock to Mud turned out, though I suppose I shouldn’t be; the volume of effect of Transmute is 30 times that of Wall of Stone. It’s also much less useful at sudden battlefield walls, so it’s not really a problem that it’s better at constructing permanent walls when you hire 3,000 men to drag mud around.

do you have the D@W playtest? because it specifically addresses how a wizard can contribute.

His answers are pretty awesome, though. I love that he calculated it down to square footage costs.

uh oh, sounds like my supplemental rules folder is getting a new .txt file :stuck_out_tongue:

I do not; I missed the kickstarter for it.

I suspected the rules might be in there, but decided to go ahead with the math anyway >.>

Double posting because I can’t edit!

Thanks! I love ACKS because I can do things like this and find secret math already there in the rules that I just need to extrapolate out. (For example, in other systems, it might cost more than .02 GP per cubic foot to excavate a moat and less than .02 GP per cubic foot to excavate a 10 foot pit. In ACKS? Doesn’t matter what you’re digging, digging a hole costs .02 GP per cubic foot!)

they may not be at that stage yet (or might not be doing it) but i was able to get a playtest copy of the player’s companion for pre-ordering even though i missed the kickstarter. Keep your eyes peeled and you might yet have a chance to get in on this.

Indeed, I’d done the same thing - discovered ACKS right after the PC kickstarter. I still wonder what wonderful things I’m missing not having known about them during the original core rules KS. :slight_smile:

There’s also some extra bits about using Transmute Rock to Mud and then Move Earth to “fill in” what are essentially concrete forms made of wood, then dispelling the Transmute, and boom, stonework. Doubles the construction rate.

That section did not mention additionally using Wall of Wood to help create the forms, however, which is a really good idea, though I don’t know if the physics of the Wood Wall would allow for holding the weight of the mud, though it could certainly be shored up by a construction crew before the mud comes in at lesser cost/time.

And now that I referenced it, it lists Wall of Stone to make the mudforms. So your math will not be in vain, as using Wall of Wood would be better, as that’s a different level of spell (4th) - Transmute Rock to Mud and Wall of Stone are both 5th level, so you can get more mud using Wall of Wood instead if you wait a moment to let the workers shore it up.

And now that I’m thinking about it, placing a Wall of Iron in the middle of your form, then filling it with mud and mud-to-stoning that would be an awesome surprise for a sapper team.

However building a castle with wall of X is a bad idea…one Dispel Magic and…poof, there goes your structure.

It’s certainly a risky idea, but it’s not quite as silly as you suggest.

By my reading, Dispel Magic affects a single casting of Wall of X per cast of Dispel Magic (you can cast it on a single creature or object, or a 20’ cube, none of which will get you more than one wall; I don’t think of a 60’ high castle wall made out of a hundred or more separate pieces of stone fused together as being a single object).

It is likely that the Dispel Magic will have a failure chance. At minimum caster levels for both (9th level for Wall of Stone and 5th level for Dispel Magic), this failure chance is 20%. So on average, every six castings of Dispel Magic will wipe out five castings of Wall of Stone.

As written, Permanency cannot be cast on Wall of X because it is already permanent. Personally, as a Judge, I would allow it, because the intent to me seems that you cannot make permanent those spells which have no lasting effect in the world. If this is allowed, only a spellcaster of higher level can dispel it. (Though it does increase the cost and time significantly and you probably end up losing a lot of both gp and time. But hey, if you want to make yourself 300 scrolls of wall of stone and 300 scrolls of permanency, then run out and Daern’s Instant Fortress up a castle, more power to you.)

Finally, unless magical construction is so common in your world that it’s worth casting Dispel Magic on random castles to see if they fall down (and I don’t see why it would be, since it’s much more expensive to hire a mage than it is to just have the work done), the enemy would need to know that it was created by magic. (Different PCs will have different ways of ensuring that the construction workers don’t talk, of course, and some of these will be more effective than others.)

Overall, I agree with you that this is a risky tactic that does not give you sufficient advantage to overcome the risk in most situations. You’d need to want something specifically about the differences (maybe you actually don’t have the GP and you don’t need to pay your own character, or maybe those two days are really vitally important) and be willing to accept the risk of dispelling for this to be a good idea.

While dispel might not make the whole thing go away, a 20’ gap in a defensive wall negates the entire benefit of the wall in the first place. A missing support wall or two in a tower could cause the whole thing to crumble and kill everything in it.

And while it might be expensive to hire a mage to throw some dispels I bet it’s cheaper and quicker than a whole team of siege engines.

As you say, there might be times it’s worthwhile…but damn you are taking a big risk.

sounds more like something fun for the PCs to “discover” about their seemingly impossible to beat enemy’s castle than something for them to do themselves.

I would certainly never risk it as a Pc!

I don’t think I’d ever want to secure a domain with a castle that I built out of walls of stone, but if, for example, an enemy army breached my castle walls then was defeated, but they have reinforcements on the way, I would seriously consider using walls of stone to shore up the defenses. (Similarly, maybe there was never a castle here at all, but the enemies will be here in a month and I need my defenses in place as quickly as possible.)

A dispellable wall is better than no wall at all.

I can definitely think of circumstances where a magically-erected castle or other fortification would be worth the risk: if your choices are putting up such a magical castle in a few weeks or not having any kind of fortification, then the risk may be worth it.

an interesting thought experiment: could you build an “instant castle” spell using the spellpoint system in the PC? I think if the conjuration/transmutation sections had modifiers for a casting time of 1 hour or a casting limit of once per day/week you might be able to make something cool.

Speaking of the custom spell section, has anyone tried to make elements for a “Builder mage” with custom spells that could further contribute to castle construction?

After doing this, one of the things I wanted to do was see what a Daern’s Instant Fortress type magic item would cost to make.

Since I know what wall of wood and wall of stone give you for GP value per spell level, I can derive what spell level the ‘create furnishings and all other costs’ spells should be, then figure out how many spells have to be cast to manage it. (Wall of Stone gets you 250 gp per cast, which is 50 gp per spell level; Wall of Wood gets you 150 gp per cast, which is 37.5 gp per spell level; a little bit of averaging and rounding gives us 45 GP per spell level for our Create Furnishings And Other Castley Bits spell). For a random selection, let’s say it’s a 4th level spell, so it makes 180 GP worth of furnishings per cast.

A small tower costs 15,000 GP. I’ve actually realized that my original tower math might be wrong; I’m using a 20’ outer diameter in the original post, which gives you a pretty tiny tower inside. With a 20’ inner diameter, the outer diameter is 30’ (5’ of wall on each side), giving us radii of 15’ and 10’. This gives us 11, 780 cubic feet of stone in the tower; 12 casts of wall of stone will reduce the cost by 2,945 GP.

This means we need to cast our other spell a total of (15,000 - 2945)/180 = 67 times.

Our Daern’s Instant Fortress can therefore cast 12 5th-level and 67 4th-level spells. Extrapolating from the magic item table in ACKS, I would say that an item usable 1/month costs spell level * 500 * 4, and an item usable 1/year is spell level * 500 * 2.

The base cost, before usage modifiers (spell level * 500 being base) for our Instant Fortress is (67 * 4 * 500 ) + (12 * 5 * 500) = 164,000 GP. That’s what it would cost to make it a one-use item. Usable 1/year, it would cost 328,000. Usable 1/month, it would cost 656,000. Usable 1/week, it would cost 984,000.

On the plus side, the magical research throw is only penalized by the level of the spell, so a sufficiently rich mage is actually capable of creating this item, and as a one-use item, its price is low enough that it might actually be doable, especially once you have a formula of it. I don’t think it’s very likely that it would be worth investing in one usable more than 1/year, but it might be worth it to go for the 1/month version if you’re a ridiculously rich and bored Emperor.

Do you take into consideration the craftsmanship required to make those things is different? Laborers can erect walls but furnishings (that aren’t garbage) require more talent (I.e. more expense costs in creation).

Presumably those things are already included in the cost of the tower.

I agree that the 180 gp worth of furnishings would be many fewer cubic feet of wood than the 150 gp worth of wooden palisade that a wall of wood spell creates. But one of my core assumptions of the math under this entire thread is that the cost listed in the book includes everything.

So the 15,000 GP cost for a tower includes the skilled craftsmen necessary to hang the doors properly, build real chairs and tables instead of just slapping chunks of wood together, buy and transport rugs, and so on. The furnishings created by a single casting of Create Etc would probably be worth much less than 180 gp if sold (even to people who didn’t know that they’re dispellable), because the casting also includes the cost of transporting them to the site and putting them in place as well as simply creating them.

That said it would be reasonable to reduce the GP value created by Create Etc, because you are right, it’s a more complicated task than walls are. (I didn’t really put a lot of effort into designing or balancing the Create Etc spell because to me, it’s more important to have an algorithm than the specifics; I now know how to calculate the cost of an item that creates this sort of thing, and I can plug in any number I want for the specific GP value created per casting.)