Medieval Demographics in Brief

When I’m developing a wilderness map, I always have to decide, “At what frequency should I place villages, cities, and castles here?” Below you'll find a short document that I've drafted on research for a model on medieval-level demographics. Of course, I'm not the only person to do this, and in fact I don't think this is the only time I've done this; but the document includes copious endnotes so I hopefully stop re-doing this and forgetting which parts are based on real-world data, and which parts I made up for the game.

Here's an executive summary. We use as the basis for our model data from England around the 11th or 12th century;  the population then was around 2 million. (Earlier in the Dark Ages it might have been half or one-quarter this level; later in the High Middle Ages it would be around 5 million, and then collapsing back down to 2 million at the time of the Black Death.) For our baseline in history we find, in round numbers:

1. Cities: One per 1,000 square miles.
2. Castles: One per 100 square miles.
3. Villages: One per 10 square miles. 

(When we say "cities" here we really mean any walled towns.) A variety of examples from Gygaxian rulebooks shows a markedly less dense population, by roughly an order of magnitude (about 10 times fewer features per equivalent land surface area). For game campaign maps, this author is currently using a value about halfway between the two, that is, about one-quarter the baseline medieval population density (i.e., Dark Ages levels). More precisely, we assume that only about one-quarter of the land area is inhabited by humans, with density in those areas approximately the same as medieval England (the rest of the map is left over under the control of various nonhuman races and monsters; in particular, almost any non-plains locations). Therefore this author currently uses, for fantasy realms:

1. Cities: One per 4,000 square miles.
2. Castles: One per 400 square miles.
3. Villages: One per 40 square miles.

This can easily be converted to a recommendation or average on a game map per-hex basis with a little math. Note that the area of a hexagon is \(S^2 \cdot \sqrt{3}/2 \approx S^2 \cdot 0.866\), where \(S\) is the length of the hex measured across opposite edges. (For example, a 24-mile hex is close to 500 square miles; a 6-mile hex is about 30 square miles.) We currently use something like the following map scales:

1. 100-mile hexes: Shows capital Cities (1 per 30 hexes).
2. 24-mile hexes: Shows walled Towns (1 per 8 hexes)
3. 6-mile hexes: Shows baronial Castles (1 per 12 hexes)
4. 1½-mile hexes: Shows individual Villages (close to castles)

We can otherwise express this by stating that, on average, at Level 1 there is one walled town per hex; at Level 2 one castle per hex; and at Level 3 one or more villages per hex, and therefore these features are not shown on the maps at those scales. The 6-mile hex scale is expected for use in standard wilderness adventure and exploration (smaller sizes permit the entire map to be crossed in a single day, and are generally only used for introductory level adventures, or for added flavor, not strategic movement). We emphasize that at this exploratory level, it makes no sense to depict individual villages (historically, there would be multiple villages per hex); instead, we place castles as shown and assume that each of the adjacent hexes has between 1 and 3 villages in fief (within range of daily patrols, or for a runner/rider to get help within an hour or so). We further assume that the villages mostly have no amenities of interest to PCs (inns, taverns, general stores, etc.) In general we find this makes for attractive and gameable maps, with plenty of space left over for exploration and monster lairs.

Finally, populations for each of the urban features can be simply approximated by the following (this generally hews pretty closely to both historical data and classic D&D rules):

1. Cities: 10,000-60,000 people.
2. Towns: 1,000-6,000 people.
3. Villages: 100-600 people.

A further research question might be this: Is the population scarcity shown in the writings of Gygax consistent with other works of fantasy literature? While likely harder to quantify, this author would hypothesize so. (Consider: Featuring only a single central city in an area that would historically have several, needing to focus the narrative on a few key features, etc.)

See full details in the document below, with appropriate research citations (PDF):

Medieval Demographics in Brief