Great Cities--Not that Old?

Idle thought: it just struck me that a lot of world-class cities--the kind we think of as having been there forever--are not that old.  Athens, Jerusalem and Rome are old enough, I guess (though Rome may count as a relative latecomer).  Also London.   "New world" cities like New York and Los Angeles--by definition, "new" (so also Sidney, Perth, etc).

But consider Bombay Mumbai. I suppose there were "always" people on those islands, but it didn't really get any traction until 1661, when Charles II got it as a wedding gift: the English/Brits liked it as a trading port. Which explains also Shanghai and Hong Kong, albeit much later. And if the British use tradidng ports to force their way in, recall how Peter the Great created St. Petersburg Leningrad Petrograd St. Petersburg to force his way out.  I suppose there are a hundred more examples that haven't come to mind just yet.