Low-Tech Kingdom Population Density?

[Sunrunners_Fire]

Originally Posted by Polydamas

I personally suspect that the population required to maintain TL 4 in isolation is in the tens of millions (see: Hellenistic/Roman Mediterranean, Tokugawa Japan). You can have towns and muskets with a much smaller population, but not amazing art and huge libraries and cities with hundreds of thousands of people and pocket multitools and large amounts of good steel armour and all kinds of specialists and ships of a thousand tuns burden. So you will need much more land, or a lower TL.

What then do you consider the minimum population to maintain TL 4~?

Not develop it (as they didn't develop it themselves in the first place), but maintain an existing body of knowledge and the infrastructure necessary to make use of it?