Demographically, the Roman Empire was a premodern state. There was a high infant mortality, low marriage age, and high fertility within marriage. According to A.H.M. Jones (Later Roman Empire, 1954, vol. II, p. 1041) "The death rate was uniformly high at all ages from ten, below which we have no reliable data"..."the infant and child death rate would have been very much greater than for adults. The female death rate was substantially higher than the male, especially in the child-bearing years. Thus in Africa, of 100 boys of ten 85 survived to 22, 74 to 32, 58 to 42, 47 to 52 and 36 to 62. For girls the corresponding percentages were 73, 54, 47, 39 and 28." These figures correspond to those arrived at by Bruce Frier in Bruce W. "Demography", in Alan K. Bowman, Peter Garnsey, and Dominic Rathbone, eds., The Cambridge Ancient History XI: The High Empire, A.D. 70–192, (Cambridge: Cambridge University Press, 2000), 827–54. Of those still alive at age 10, half would die by the age of 50 according to the African statistics cited by Jones, ibid. Roman women could expect to bear on average 6 to 9 children.. Life expectancy was in the mid-twenties. Of those who reached the age of 22 52% of men reached 52 and 39% of women reached the age of 52. The population curve was heavy at the bottom: the median age of the population of 0 million was 25 more or less. This has importance when considering the numbers of men eligible for military service from age 18 to 45 - on the face of it they were 20 percent plus (there were more males than females) of the population, 15 million(?), but the minimum height of 165cm (5 Roman feet, 7 inches) for rank and file new legionary recruits and the even greater one for elite units eliminated half of them; unfit for service more, and 2.0 million had to be subtracted because they were slaves who were seldom pressed into service except in extreme emergencies leaving 5 million fit for service (of 13 million free men 18-45), i.e. 1 in 10 of qualified men had to be in the armed forces if these numbered 500,000. The pressure was partly relieved by enlisting men from outside the Empire (the so-called 'barbarians') to fill up the ranks which needed 40,000 recruits a year (half of whom had died before the end of their 20 and 25-year enlistments). These taken from a relatively small pool of voluntary and eligible recruits, 2.5 million, between the ages of 18-32.
At its peak, after the Antonine Plague of the 160s CE, it had a population of about 60–70 million and a population density of about 16 persons per square kilometer spread evenly. However, the populations tended to be gathered in river valleys and areas suitable for cultivation; and in 2000 towns and cities. In contrast to the European societies of the classical and medieval periods, Rome had unusually high urbanization rates. During the 2nd century CE, the city of Rome had more than one million inhabitants. No Western city would have as many again until the 19th century.
For the lands around the Mediterranean Sea and their hinterlands, the period from the second millennium BCE to the early first millennium CE was one of substantial population growth. What would become the territory of the Roman Empire saw an average annual population growth of about 0.1 per cent from the 12th century BCE to the 3rd century CE, resulting in a quadrupling of the region's total population. Growth was slower around the eastern Mediterranean, which was already more developed at the beginning of the period, on the order of about 0.07 per cent per year. This was stronger growth than that seen in the succeeding period; from about 200 CE to 1800 CE, the European half of the empire only saw about 0.06 to 0.07 per cent annual growth (Europe as a whole saw 0.1 per cent annual growth rates), and the north African and west Asian parts of the empire saw almost no growth at all.
By comparison, what is now the territory of China experienced 0.1 per cent annual growth from 1 CE to 1800 CE. After population decline following the disintegration of the western half of the Roman state in the fifth and sixth centuries, Europe probably re-attained Roman-era population totals in the twelfth and thirteenth centuries and, following another decline associated with the Black Death, consistently exceeded them after the mid-15th century.
There are no reliable surviving records for the general demography of the Roman Empire. There are no detailed local records, such as underlie the demographic study of early modern Europe, either. Large numbers of impressionistic, moralizing, and anecdotal observations on demography survive from the literary sources. They are of little use in the study of Roman demography, which tends to rely instead on conjecture and comparison, rather than records and observations.