How many people lived in the city of Rome at its peak?

How to get close to this number

Bound it by the food supply. A pre-industrial city can only be as large as the grain it can import and distribute, and Rome drew on a Mediterranean-wide supply network with state-organised shipments. That logistical ceiling is what produced a city of around a million, and no city without comparable logistics reached it.

The comparison in the explanation is the one that conveys how exceptional it was: no European city matched that size again for roughly sixteen centuries. That is not a slow recovery; it is a collapse in the underlying capacity — the supply networks, the aqueducts and the administrative machinery all disappeared, and urban scale went with them.

Ancient population figures are reconstructions from grain distribution records, building density and the area enclosed by walls, none of which gives a headcount. Estimates for this city have ranged from half a million to well over a million across the historiography, and the figure quoted represents a scholarly consensus rather than a measurement.