Suffice to say these three cities existed in different times and very different places. But questions of health, food storage/preservation and water distribution, waste disposal, and justice make me wonder how they managed to remain functional.
Rome’s population was sustained by grain shipments from different regions. North Africa, Sicily, and Egypt were all serious food producing regions of the Roman Empire/Republic. Rome was entirely dependant on these shipments by boat for food. The decline of Rome as a city, in part, was due to them losing North Africa to the Vandals, Egypt to the Eastern Empire etc (as well as many other reasons)