After the fall of the Western Roman Empire, the population of Rome shrunk drastically, and afaik it took centuries until it regained its original population and geographical sprawl. When did the "modern" Rome become as large as the ancient one?
My friend who is browsing with me atm believes its post 1900 but can't remember where he is getting the info from so will try to get back to you on this. I guess it partially depends which population estimate you are using?