system
A chat on 4chan
human
Because I´m an archeologist and it´s not a matter of believe, really.

We still find 'lost cities' of more recent civilisations, civilisations that we DO know about. Forgotten civilisations might very well be just city-states with cities barely the size of your average-sized european village. 

I don´t even doubt that there are dozens of these still left undiscovered, dissimilar enough to what we know to be counted as 'new civilzations'
gpt
What I´m trying to say, is that it´s a matter of perspective. A civilization does not have to be continent-spanning. Hell, look at the current world, in a few hundred years, given the right circumstances, countries like Liechtenstein would be counted to any of the bordering coutries until decades of research would proof it different, yet it absolutely is its own thing in the current world.