That urbanisation estimate is deeply flawed (the wikipedia entry even claims a higher percentage than the source it cites): don't believe everything you read, least of all on wikipedia. The claim that Roman urbanisation was "twice as high as that of Europe at the turn of the 19th century" (an assertion likewise not made by the cited authors) rests on combining a thus inflated Roman percentage (with places as small as 1,000 inhabitants reckoned as "urban") with a far more conservative one for later Europe (here probably with a lower limit of 5,000): applying a common definition they seem about evenly matched, with Europe c.1800 probably slightly ahead - itself a remarkable finding: Rome in this respect needs no exaggeration.

The claimed million for the ancient city of Rome is itself problematical: there are sources indicating such a total, but there's also a good case for a lower figure on the basis of area and likely densities. These estimates are far from settled. Beware the lure of big-looking numbers.