The Roman Empire's population has been estimated at between 59 and 76 million in the 1st and 2nd centuries, peaking probably just before the Antonine Plague. Historian Kyle Harper provides an estimate of a population of 75 million and an average population density of about 20 people per square kilometre at its peak, with unusually high urbanization. During the 1st and 2nd centuries CE, the population of the city of Rome is conventionally estimated at one million inhabitants. Historian Ian Morris estimates that no other city in Western Eurasia would have as many again until the 19th century.