I have been conducting research into the Late Middle Ages for a novel I am working on (some of my questions actually being answered by a few posts to this forum/thread/insert proper term). I have seen the Mega-Tutorial on Worldbuilding Medieval Towns, Cities, Population, Professions, Armies, Technology, Justice, and Trade! (link to the post: https://www.reddit.com/r/worldbuilding/comments/4byhle/megatutorial_on_worldbuilding_medieval_towns/ ). In this post, it mentions a rough-estimate guide of one castle/citadel/fortified structure per 50,000 people. That number seems considerably low to me, as the frequency of castles in medieval England breaks that.
I've seen an estimate of 1,500 castles in England, and the peak population for England in the Middle Ages seems to be between 3.5 and 7 million. At the high end of 7 million, that comes to one castle for every 5,000 people (generously rounded-up from 4,666).
For Germany, the population estimate is 7 to 10 million people. In the book I just picked up (German Medieval Armies 1300-1500, by Christopher Gravett on the Osprey Men-at-Arms series), it mentions an estimate of 10,000 castles in Germany by 1300 CE (page 4, paragraph "By 1300, there was little crown land left...", 5th sentence). At the high end of 10 million people, that comes to one castle for every 1,000 people. (However, the book doesn't specify whether by 'Germany' it means 10,000 castles within the Holy Roman Empire of 1300, or within the borders of modern-day Germany in 1300.)
I will gladly admit I haven't delved too much into this. Does anyone out there have any better-informed statistics, and can help provide a rough average on the number of castles per population? For this question, lets set the definition of a castle as a fortified home, designed for refuge of people when required and used for governance in peace times, excluding any fortified home belonging to a monastery, church, or other religious facility.
Any help would be greatly appreciated, and very helpful in 'filling-out' the map for the world I've created with any smaller castles that aren't significant enough to be shown (they are definitely significant, just not enough for a zoomed-out, 'summarized' map of major locations.)
Edit: I left the last paragraph about posting to AskHistorians in before I decided to just post this here instead of on r/worldbuilding. Oops xD
Hi, I wrote a bit here about castle functions and more specifically how, despite popular misconceptions, they really aren't designed to function as sites of popular refuge.
With that in mind, it's somewhat of a wild goose chase to try and correlate castles with population figures. Rather, correlate the role of the castle with the terrain and the political context. Castles proliferate rapidly in England in the wake of the Norman Conquest precisely because they stand apart from the general population: they provide an effective means for a relatively small and unstable Norman elite to project power across a largely hostile population. A further wave of castle proliferation occurs during The Anarchy of the twelfth century as the political instability and lapses in royal authority encourage nobles to build castles both for protection and to increase their own power. Indeed much of the early part of Henry II's reign sees the forced dismantling of 'unauthorised' castles which would have allowed nobles to challenge royal authority.
In more lowland and central areas of England, castles would be relatively spread out, and many villages and even towns might not have a nearby castle at all. Castles were clustered much more heavily in The Marches, the border areas with Wales and Scotland. Here, more trusted nobles were granted much more contiguous stretches of land to ensure both a more effective defence and more opportunity for expansion. In this context, castles would be built far more densely than might otherwise be suggested by the local population densities in order to properly extend control over strategically important areas and to encourage colonisation of these regions.
Hi there - we're happy to approve your question related to your novel, and we are happy for people to answer. However, we should warn you that many flairs have become reluctant to answer questions for aspiring novelists, based on past experience: some aspiring novelists have a tendency to try to pump historians for trivia while ignoring the bigger points they were making, while others have a tendency to argue with historians when the historical reality does not line up with what's needed for a particular scene or characterization. Please respect the answers of people who have generously given you their time, even if it's not always what you want to hear.
Additionally, as amazing as our flair panel is, we should also point out that /r/AskHistorians is not a professional historical consultation service. If you're asking a question here because you need vital research for a future commercial product such as a historical novel, you may be better off engaging a historical consultant at a fair hourly rate to answer these questions for you. We don't know what the going rate for consultancy work would be in your locality, but it may be worth looking into that if you have in-depth or highly plot-reliant questions for this project. Some /r/AskHistorians flairs could be receptive to working as a consultant in this way. However, if you wish for a flair here to do this work for you, you will need to organize this with them yourselves.
Another previous post that you might find extremely useful is this one
Where /u/mormengil goes into quite a lot of detail about a specific castle in south eastern France, their scale, cost and how they fitted into both society and the larger defensive 'system'. Well worth a read.