The biggest city on Almea is Inex, with just over 600,000 residents.
Verduria city is close behind.
After that come Curau and Ṭetäs with over half a million each.
There's quite a few populous Xurnese cities, but the next city with a firm figure is Jansɛ, capital of Belsao, with over 300,000.
These numbers may seem a bit disappointing, but that's because we're used to living in a much denser world. Ancient Rome had only about 250,000 people, and the first European city to reach a million was London, around 1800. Beijing reached a million at about the same time.
I know you have sources for this. However, just to be clear, it should be said that these estimates are far lower than mainstream ones. As a basic cite, wikipedia cites "Daily Life in the Roman City" (published 2004) as summing up the estimates: absolute minimum of 200,000, maximum of about 3.5m, most historians go for a bit over 1m.
We know that there were 320,000 inhabitants of Rome on the dole. These were all adult male free citizens. Including women and children, this easily gives a population of over a million, and that's assuming that everybody who could be on the dole was. On the other hand, it's possible to posit massive fraud in order to get a very low figure, or more reasonably to suggest that there was a large male migrant worker population, and/or a veteran population, that skewed the gender/age/freedom balance, in order to give only a moderately low estimate.
We also know that Rome in the 4th century at one point had 1,782 private homes, and 43,580 apartment buildings. Your estimate thus requires no more than 5 people per apartment block, and small families in the private homes - which seems unlikely. Or massive purposeless fraud - you'd expect the government to undercount the houses if anything, not overcount them.
Finally, we also know that the inhabited area of Rome proper was 1370 hectares. Your figure would seem to assume an awful lot of parkland and low-density housing, in contrast to the reports of ten-story apartment blocks densely packed together.
Alexandria, Changan, Baghdad and Beijing are all widely thought to have passed 1m too - and maybe Kaifeng, Hangzhou and Jinling as well, though they seems more questionable.
Anyway, you may not find this convincing - I know you've explained your theory in the past. But just to add some context to what you're saying, I thought I should add in the more common view.
But the river tripped on her by and by, lapping
as though her heart was brook: Why, why, why! Weh, O weh
I'se so silly to be flowing but I no canna stay!