[inglor_cz]

Rome during Trajan's rule had over 500k and maybe even 1M people, and ruled half of Europe.

But I would still say that it was a less advanced civilization than Europe in 1500 AD. Trajan's Romans weren't able to sail the oceans, print books, didn't know what gunpowder was and could not use positional numeric system to actually calculate things in abstract; their way of counting stuff was the abacus, which sorta works for everyday tasks, but you cannot develop any higher maths with it. Even steel was non-trivially worse in Roman times than in 1500 AD.

All of that was meaningful progress. Sure, some knowledge was lost (Roman concrete, Greek fire). But much more has been acquired.