Quote Originally Posted by Martin Greywolf View Post
Your first problem. It's not that cities didn't exist in early medieval period, it's that they were extremely rare, with very few exceptions that were mostly in Romen empire remnants of some sort (parts of Outremer, Byzantium, Greek cities, Rome itself). Early medieval Florence has 1 000 people in it, while Constantinople has 150 000, Rome 80 000, Thessaloniki 40 000, Poitiers has 8 000 (this being one of the largest cities in one of the most arable areas of Europe). Sure, Luozang has half a million at this time, but that isn't early medieval, the term applies to Europe and Europe only.
This is part of the reason I asked the question, actually. I basically want the city as small as possible while still able to keep up the sacrifices.

Quote Originally Posted by Martin Greywolf View Post
The only way to fix these bottlenecks is to magic your agriculture into being way, way more productive - maybe that's what the sacrifices are for?
That is indeed part of what they're used for. I haven't decided on the details but it'll probably be something like super-efficent farms close to the city or possibly some sort of magical hydroponic farm.

Quote Originally Posted by Martin Greywolf View Post
Your immediate problem is, why is it a city then? The most plausible reason is probably a ramnent of a bygone empire, but it could be the one and only city-state left from the late stone age that actually figured out how to run a city state - that is no small task, a few would-be city-states probably floundered there.
That one I have covered, at least. While the sacrifices provide all sorts of useful magic, the main reason for them is to keep out the nasty things living outside the city. I won't go into details (and I haven't decided all of them) but basically it's rather dangerous to travel outside the city, not to mention live there. Enough that living in a city with regular human sacrifices is worth it to most people.

Quote Originally Posted by Martin Greywolf View Post
tl;dr If it is large enough to qualify as a city and has the corrseponding historical population, the 12 sacrifices per year are a drop in the bucket.
Good to hear. That was my own guess on the matter and most answers seem to point the same way. Thanks.