I think to choose only one city which were the representative of mankind in that age would be impossible to do today... the developement of the world greatest cities is not so different from one to another to say that there is only one city which could represent all the mankind... there are different things that are considered important (as technology, culture, history, etc) and this things are spread around the entire world. It is not like in the ages of Greece and Rome, when everything was centralized in only one city and country... today everything is much "globalized", and so more equal, less "important" than everything else...