Demography of the Roman Empire

Papyrus evidence from Roman Egypt suggests like other more recent and thus better documented pre-modern societies, the Roman Empire experienced high infant mortality, a low marriage age, and high fertility within marriage. Perhaps half of the Roman subjects died by the age of 10. Of those still alive at age 10, half would die by the age of 50.

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.

Due to migration, the ethnic composition of the city of Rome, Italy, and the empire as a whole went through substantial change during the early and later stages of the empire, with the migration divisible mainly into two separate periods: first during the Principate, with immigration originating from Eastern Mediterranean and the Near East into the core of the empire in Latium, rendering the European natives there a minority; and a second period starting with the Dominate, entailing immigration by barbarian peoples from Central and Northern Europe into Italy and Latium, continuing past the collapse of the Empire, throughout the medieval ages and the early modern period.