Dungeons in a Medieval fantasy

Question

Suppose the typical Medieval fantasy world with elves, humans, dragons, magic, politics, society, and the rest, such as is found in countless open-world games. Open-world games encourage the player to fill in all the corners of the map, leading to the exploration of countless dungeons in all their various forms.

We've already discussed the economic impact of heroes clearing and looting dungeons. We've identified that this sort of dungeon-laden world is possible, under the right conditions. There's also been a discussion about what society would look like if monsters could appear as random encounters.

What we haven't discussed, and I am asking the community here, are the following two questions:

1. What is a reasonable occurrence of dungeons in a typical Medieval fantasy world?
2. What is a reasonable amount of time for a dungeon to "repopulate"?

For the purposes of this question, "dungeon" refers to any of, but not exclusively, the following: shallow cave, deep cave, abandoned outpost, ancient fort, lost temple, ruined settlement, verdant grove.

Answer 1

What is a reasonable occurrence of dungeons in a typical Medieval fantasy world?

In theory you could have several dungeons (as defined in the question) on top of each other or only a few in the whole world. It depends on climate and sources of food.

If we look at John Ross text using late-medieval France as a default, it is suggested that "square mile of settled land (including requisite roads, villages and towns, as well as crops and pastureland) will support 180 people". The text also mentions that not all land is suitable (for settlement that is) making the average density for bigger areas considerable less, and (as pointed out in comments) "The French were blessed with an abundance of arable countryside".

Anyhow, if the dungeons inhabitants are living of raiding the surrounding land, the number of non-raiders will after a while (or in worst case: immediately) be lower to account for the resources taken by raiders. When enough resources is taken by raiders, the non-raiding population can not sustain itself, or will get fed up and do something about the raider-problem.

But what if the dungeon is self-sustaining? Well in that case we could have "infinite dungeons" (as long as we can build a "deeper" cave), but will need some sort of magical or non-magical energy/food source. The amount of farmland needed per person depends on circumstances. This becomes even more complicated when we take into account that the farming will take place in caves, that might or might not have magical radiation, one would have to imagine that the plants chosen does not use photosynthesis (such as mushrooms), rain does not fall directly on the crop and so on.

Regarding dungeons that consist of ancient ruins, I imagine that these are populated by the undead or wild animals, but once where populated by humanoids. It does not have the same need for food supply, but rather a need for explanation. Maybe the ancient ruin got caught in a earthquake/curse and the city moved a few hills over, or maybe the whole ancient civilisation collapsed and places of lesser importance in the relative post-apokalyps become abounded and relatively forgotten (imagine Machu Picchu). If all ruins are meant to come from the same lost civilisation one could model the city density of the civilisation to get the ruin density. If a ruin is close to active settlement, there must be some reason for people not going over to dismantle the ruins when they need materials. Such reason as the undead, curses or difficult terrain.

What is a reasonable amount of time for a dungeon to "repopulate"?

Again, in theory it could take days or they could never repopulate. It depends on how attractive the living space is and how dense the population is in the surrounding area.

A raider cave could be repopulated in a matter of weeks or even days, as long as there is beings that want to raid that can catch the rumour that the "district" close by (or further away if directed by a Dark Overlord) is empty. If they bring some resources (and gain some on the way) it would not take long to settle in.

Similar for self-sustaining dungeon that is part of an cave ecosystem. Maybe the surrounding tribes of similar humanoids used to trade with the affected dungeon for a certain type of mushroom, and now find themselves with opportunity to take over the whole mushroom cave.

But on other hand maybe that particular cave had a bad reputation, the raiders where the only ones desperate enough to live the raiding life and/or the dungeon have nothing more desirable left except the living space itself. Then it is probable that, aside from a few wild animals, the dungeon will be left alone to the ghosts.

If we are going by repopulation by population growth alone, it could take a long time. Medieval population growth is affected by harsh conditions such as famine, and fatal illness. High birth rates and high death rates, gave a small increase over time. If the dungeon-dwellers have a faster reproduction rate than humans, population growth will be more viable.

Answer 2

As far as I can tell, the main consideration you have to make for your dungeons is how they're getting food. It's possible that a dungeon sits atop a well of magical energy that constantly sustains its demons and slimes, but that is somewhat beyond the scope of this site. So let's assume you have some flesh-and-blood mortal creatures in your dungeons.

Now you've got three options: hunt and gather, farm, or get resupplied by a third party. I've ordered these by the amount of space they'll need per NPC: if the dungeon's residents are hunting and gathering to survive, not only will they need a lot of land to be sustainable, but there probably won't be too many people actually in the dungeon at any time (except at night maybe). Farming will be a little bit easier, but you'll still need a lot of space to sustain the number of creatures you'd expect to fill a dungeon.

So if you want your dungeons surrounded by lush wilderness, but also with enough nearby dungeons that you aren't riding on horseback for days to get to the next one, you're going to need to go with the third option of getting supplies from somewhere else. This option is best because not only do your dungeon's NPCs not need to go outside to get their food, but this also provides a good way for 'respawing' to happen.

Look at it this way: some rival empire or the Lord of Darkness or whatever decides to take over a dungeon as part of some nefarious plot. In order to keep the dungeon manned, they'll need to keep on sending supplies: the food is still being produced somewhere, but rather than putting fields in your characters' fields of view, all that's necessary in the vicinity of the dungeon is a series of roads. Every few weeks (or less, depending on how close the dungeon is to its source of supplies), the new resupply convoy arrives, inspects the dungeon, and goes back to get whatever is needed in the next resupply run. If your heroes cleared the place out, the next resupply will include a new batch of enemies to take the places of those that were killed.

With this method, you can get a lot of dungeons that are pretty close to one another, and can get repopulated in a matter of days or weeks. Of course, more dungeons controlled by the same guy means more farmland and other infrastructure somewhere in your world, but you don't have to make it nearby, so long as there are open supply lines.

Answer 3

If you're assumptions are based on dungeons being created by "strange reality" or a "conjuring field" (from the links you provided: https://worldbuilding.stackexchange.com/a/268/2488 and https://worldbuilding.stackexchange.com/a/13645/2488), then the answers to your questions just depend on whatever laws of the reality/fields you want to go with. Since you can define whatever laws of magic you want to go with, it's a good idea to work backwards from what you want the world to be like.

Want the world to have more epic heroes, more magical items, more professional dungeoneers? --> Then go with more dungeons and faster repopulation. Want the world to be more realistic? Want monsters and magic to be more mysterious and rare? --> Then have less dungeons and slower repopulation.

Answer 4

The first thing you need to consider is what causes it to become a dungeon rather than just being an empty cave.

If there's some sort of energy source (portal to netherworld etc. hereafter called a source) that attracts monsters then you'll have a repopulation rate based on how powerful it is. If it also feeds the monsters and causes them to become more powerful (to a limit based on monster type and power of source) then you can also have them back up to full power in a reasonable amount of time. You could say that a powerful source would repopulate with low level troggs/imps within a matter of days. They would feed on the source and become more powerful, but to a low limit as they're low level beasties. More powerful creatures would also be attracted to the underpopulated region and rarer types such as demons, dragons etc would slowly return over the course of some months.

If there was a source that emits monsters then you'll have a faster return of high level monsters displacing the low level troggs (who are merely attracted to a cave as their natural environment) to the outer regions.

In the first case you're going to have trouble repopulating loot until a few adventurers have died in there to leave their weapons and armour behind. In the second case they could be coming in with high level weapons/armour already on.

There's a third option here, the source creates the monsters from smaller creatures, small lizards exposed to it for long enough eventually become dragons. Stray dogs become corehounds. Waifs and strays who come looking for shelter eventually become [insert biped monster here].

Lost temples much as per caves with portals to netherworlds. Abandoned forts/outposts could be populated with a mix of roaming mercenaries, highwaymen, outlaws etc. These will take considerable time to return if they ever do once cleared out, people have better memories for what happened and the folk thereabouts will remember. Verdant groves will also tend to attract suitable beasties rather than relying solely on local reproduction.

Regarding density, a powerful source in a deep dungeon will have an effect over a very large area. You could have knock on effects for miles around with every cave, dark corner or overgrown woodland classing as a dungeon. Beasties tend to be very territorial, tending to end up in groups no larger than your average adventuring party, barring a few weaker types who sometimes move in larger numbers. This means that the more powerful monsters will be closer to the source and weaker ones will be pushed to the outside and are more likely to be encountered near towns and farmland. Human habitation would quite rapidly move away from a place like this as the little people at the bottom of the garden would be stealing too many children/sheep in the night. There's no practical limit to the density of small sources, I wouldn't expect a major one within two days travel of the next. Though if they're old mage towers, something horrible about halfway in between left over from the mages fighting.

Abandoned forts/outposts/temples will depend on population density. A good solid temple will only exist where there was once a good solid (human?)population. Forts and outposts may be up against borders of the small kingdoms and baronies that mediaeval Europe was broken into, up against the edge of a monster zone caused by a major source or even just on the road between two market towns. No more than one in a days travel, unless on borders where there could be one either side of the line.

With regards to what they eat, most beasties are carnivores, they'll get a good healthy diet of lean young adventurer, otherwise troggs and imps will be the bottom of the food chain for those that don't feed on the source itself.