Duneflower
Warlord
Ah, yes, thanks for reminding me: Date of foundation or acquisition.
Date of founding makes sense to some extent, but doesn't always. For example, civilizations like the Byzantines or Babylonians mostly consist of cities founded by other civilizations.
Philly is also a decent choice, and is maybe easier to argue for than New York.
I would move Haithabu up in the list, because of it's importance as a trading post. (They found coins even from islamic countries from that time at the site where Haithabu was.)
This leads to questions of accuracy. In general with the mod, I've used city names as they're generally used in the English-speaking world - Moscow instead of Moskva, Thebes instead of Niwt-Rst, etc.
You're right that Haithabu (Hedeby) was very important. The cities further up the list were founded earlier, though, and were also important.