OSR: Building Castles

Everyone wants to build castles. Nobody has good rules for building castles.

ACKS takes a very typical approach and gives prices for gatehouses, lengths of masonry, walls, outbuildings, etc.  Charles Taylor has a system for doing the same, and shows off his math in Burgs and Bailiffs. These rules have clearly been well researched. A lot of love went into them.

But I swear, if I have to pull out an excel sheet at game in order to figure out what my players are doing, I'm going to quit and play Fiasco or something.

Aydon Castle, UK

Building a Castle

So your PCs have cleared the Tomb of the Serpent Kings or the Lair of the Magenta Ocelot. All the inhabitants are dead. All the traps have been disarmed. All the gold has been looted. Now what?
In most games, the PCs move on to the next dungeon or adventure. They are walking away from a fortune. Dungeons are usually made from stone. Dressed stone

And what are castles made from?

When a dungeon has been cleared to an acceptable degree, the PCs can turn it into a quarry. If there is a suitable site nearby they can create a ready-made castle. In my system, this is the only way for the PCs to create a castle of their own. They can inherit castles, steal castles, conquer castles, and marry into the ownership of a castle... but they can't build their own unless they turn a dungeon into one.

Side Note: "Dungeons as XP" is a cool concept on paper. Dungeons as Castles is much more fun.

The Castle of Daniau the Defender

Here's a random map chosen from Dyson Logos.
Hall of Daniau the Defender

How much of that is useful dressed stone?
Or, condensed, 126 blocks.
Let's say the dungeon uses 5' squares and has an average 5' high ceiling 5'x5'x5' cube of stone. If the ceiling is higher, just double the number of stones. I'm trying to show the worst-case scenario.

The width of the outer walls of a castle varies between 20' and 5', depending on location. The height varies between 20' and 50'. If you want to build anything higher or more specialized, add 25% to either the cost or the time of construction.

Let's rearrange our squares.
The detached squares represent other levels. We've got a 20' square tower, walls that are not particularly high (5' high, 10' wide base, with a 10'  high second level and 10' towers in the corners). The inner courtyard is small but perfectly serviceable. It's a castle in miniature, a hill fort, a sturdy outpost, or a large fortified manor. And this is just one way to arrange things.

You can also split 5'x5' squares into smaller walls. Interior walls <1' thick and <10' high don't count unless the PCs are building a maze or something ludicrous.
There are lots of very good resources online for how castles look, what their interior dimensions are, etc. I don't want to list them all here. That's what the internet is for.

Foundations and Paving and Other Bonuses

You can't just build a castle on dirt, you might say. There has to be some extra stone used.

Correct. Where do you think the floor and ceiling from the dungeon went? They are your floor and ceiling now.

Other Fixtures

Loot everything. Statues to decorate a path. Doors. Iron railings. Everything in the dungeon could be dragged free and used to improve your castle. Extra items are listed on the Price Sheet (not yet published).

Calculating the Cost

For every 100 5'x5'x5' cubes of stone (~16,000 cubic feet of stone) going into your castle, you need:

1 year of time

100 laborers, who cost 5sp/month each or, 50gp per month total, or 600gp per year
10 masons, who cost 1gp per month each, or 10 gp per month total, or 120gp per year
1 master builder, who costs 5gp per month or 60 gp per year.

100gp per month, or 1,200gp per year, in incidental costs, food, temporary shelters, church services, specialists, smiths, roof tiles, firewood, and other horrible and tedious expenses.

For a grand total cost of 165gp per month, or 1,980gp per year.

You can adjust these values as needed to speed up construction or save money. The minimum time is 6 months.

You could also approximate the cost by using 2sp (0.2gp) per stone block used per year. I suggest rounding to the nearest 50 or 100 blocks instead. Having your players bicker over the exact arrangement of a corner is not fun.

If you want to use very fancy stone (obsidian, finely worked marble, aetherite), double the cost or the time.

By hiring 200 labourers, 4 masons, and 2 master builders, you could complete a 200 [cube] castle in 1 year instead of the usual two. Incidentally, a 200 [cube] castle (32,000 cubic feet of stone) is about the right size for the Chateau de Langeais discussed by Charles Taylor.

Looking back at the Land and Investments results, we can see that it's hideously expensive for small baronies to build castles. Even a medium-sized barony like Holbach, with 186gp per month in discretionary income, couldn't build a castle in a hurry.

However, any baron or landowner does have another option. His vassals owe him labour, usually a fixed amount per year. That can reduce the cost of the castle by cancelling out the cost of the labourers (50gp per month, 600gp per year). The rest is straight-up expense.

Carnasserie Castle in Kilmartin Glen.

Land and Rights

You can't build a castle anywhere. It has to be on your land, and your lord and their lord have to agree that it's a sensible idea. People from the First and Third Estates can't build castles (although you could very easily adapt these rules to build monasteries, aqueducts, etc.)

Example 1: the PCs are vassals of a local baron. They are on very good terms with him after clearing a dungeon and paying enormous heaps of treasure in tax. After some diplomatic shenanigans, a few side missions, and a lot of flattery, the baron agrees to give the PCs (or more accurately, the highest-ranked PC who belongs to the Second Estate), a gift (not a grant) of land in order to build a fortified manor.

Example 2: the Baron shoots down the idea, but he is very distracted by other affairs, and his barony is large and disorganized. The PCs build the castle anyway and appeal to one of the Baron's rivals for protection. A small war ensues.

Example 3: the PCs have been told by their lord to clear an area and build a castle there, to pacify a rebellious domain, protect a vital road, or expand into lawless wilderness. They have been granted an improved title, conditional on the creation of the castle.

This is part of why PCs pay into the feudal system. It gets them land and labour.


For every 100 5'x5'x5' cubes of stone used to build the castle, its owner needs to pay 1gp a month in upkeep to keep the roof from leaking, the stones from cracking, the rushes from smelling awful, etc. This also includes 5 servants. The cost is mostly materials. Peasant labour won't offset this cost.

Design Notes

I'm rather proud of this idea. It uses graph paper and drawings instead of excel sheets. It rewards the players for doing a normally pointless thing and completely pacifying a dungeon. And it lets them build something that they earned, brick by brick.

It also explains haunted castles, flying castles, castles with bizarre traps, castles with unusually cavernous basements, etc.

If you want an alternate take on the whole domain thing, check out Beloch Shrike's rules on Paper & Pencils. Those rules are what I'd use, or something like the, for non-feudal situations.


  1. So, how are floors done in this system? Assuming that you want to have a 2x2 5' square interior of a tower with 10' ceilings with 3 levels you'd need 12 * 3 * 2 = 72 5x5x5 blocks. We get 3 cubes of 10x10x10 inside this tower but what are the floors and roof made out of?

    1. The dungeon your mining has floors and ceilings too.

      If wood: it comes out of the 100gp / month general expenses
      If stone: it comes out of the floor/ceiling/misc bits of the dungeon you are mining.

      Very convenient! All you need to worry about, math and block-wise, are the walls.

    2. So for stone ceilings and roofs what would the price be?

    3. Free, if you pay the cost for the walls?

      If you really need to know, you could cut a 5'x5'x5 cube into five 5'x5'x1' slices and use those, so each floor or ceiling square would be 1/5th of a wall square.

      But the general vagueness of the system is designed to account for those costs. If your PCs are investing in ridiculous ceilings, you might want to add an extra fee. But that's what painters are for anyway.

    4. And you can buy interior buildings from the Price List (not published).

  2. Then you just give them that many lego bricks and they can see what they can come up with

  3. You f'n beautiful genius. The most obvious spot to build a castle from dungeon stone is right there on top of the dungeon or more securely right outside the defeated dungeon. It's in a tricky to get to spot that is still close enoughh to stuff to have been an issue, seems like a good spot for a castle.

    1. But if you can find one... you're golden.

  4. https://www.youtube.com/watch?v=pu3O70GeQFY

  5. Quick comment: if you want a per-block price, shouldn't that be 20 gp (1980/100) instead of 2 sp?

  6. One of the things this put into context is how useful spells like Transmute Rock to Mud would be due to its ability to easily make dressed stone. The fact that the conversion to mud only lasts 3d6 days means you've basically got magical concrete. Get some carpenters and labours to shovel the mud into wooden brick molds and then a few days later you have 240 5'x5'x5' cubes worth of dressed stone.

    1. That's a very good point! And you could even add rebar (as some medieval buildings added iron bars and chains into their stonework), cast arches and details, etc. You'd want to ensure the mud settled evenly without air pockets or cracks, but that's easy enough if you keep hitting the sides of the forms.