The Roman Empires population has been estimated at between 59 and 76 million in the 1st and 2nd centuries, likely peaking 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 kilometer (km2) 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 1 million inhabitants. Historian Ian Morris estimates that no other city in Western Eurasia would have as many again until the 19th century.
Papyrus evidence from Roman Egypt suggests that 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 Roman subjects died by the age of 10; of those who survived to that age, half would die by 50.
Due to migration, the ethnic composition of the city of Rome, its vicinity, and Italy as a whole went through substantial changes during the early and later stages of the Empire, with the migration divisible mainly in two separate periods: first during the Principate from Eastern Mediterranean areas; and later, beginning from the Dominate by Northern and Western European peoples, continuing throughout the Middle Ages and the Early Modern period. The resultant changes are reflected in the differences between Northern and Southern Italy to this day. The genetic distance between Northern and Southern Italians, although large for a single European nationality, is similar to that between Northern and Southern Germans.
Background
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% 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 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 0.06–0.07% annual growth (Europe as a whole saw 0.1% 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% annual growth from 1 CE to 1800 CE. After a population decline following the disintegration of the western half of the Roman Empire in the 5th and 6th centuries CE, Europe probably re-attained Roman-era population totals in the 12th and 13th centuries. Following another decline associated with the Black Death, it consistently exceeded them after the mid-15th century.
There are no reliable surviving records for the general demography of the Roman Empire, nor are there any detailed local records such as those that underlie the demographic study of Early Modern Europe. Large numbers of impressionistic, moralizing, and anecdotal observations on demography survive from literary sources; they are of little use in the study of Roman demography, which tends to rely instead on conjecture and comparisons rather than records and observations.
Mortality Life expectancy at birth in the Roman Empire is estimated to have been about 22–33 years. For the two thirds to three quarters of the population surviving the first year of life, life expectancy at age 1 is estimated at around 34–41 remaining years (i.e., expected to live to age 35–42), while for the 55–65% surviving to age 5, life expectancy was around 40–45. The ~50% that reached age 10 could expect to reach ~45–50, and the 46–49% surviving to their mid-teens could on average expect to reach around 48–54, although many lived much longer or shorter lives for varied reasons (e.g., wars for males, childbirth for females). Even if these figures rely more on conjecture than ancient evidence, which is sparse and of dubious quality, the known socioeconomic conditions of the Roman Empire indicate life expectancy toward the usual lower bound of pre-modern populations. Roman demography bears comparison to available data for India and rural China in the early 20th century, where life expectancies at birth were also in the 20s.
About 300 census returns filed in Egypt in the first three centuries CE survive. The classical scholar R.S. Bagnall and the political scientist B.W. Frier used them to build female and male age distributions that show life expectancies at birth of 22–25 years, results broadly consistent with model life tables. Other sources used for population reconstructions include cemetery skeletons, Roman tombstones in North Africa, and an annuities table known as "Ulpian's life table." The basis and interpretation of these sources is disputed: the skeletons cannot be firmly dated, the tombstones show non-representative sample populations, and the sources of "Ulpian's life table" are unknown. Nonetheless, because they converge with low Roman-elite survival rates shown in the literary sources, and because their evidence is consistent with data from populations with comparably high mortality rates (e.g., in 18th-century France and early–20th-century China, India, and Egypt), they reinforce the basic assumption of Roman demography: that life expectancies at birth were in the low 20s.
Because no population for which accurate observations survive had such a low life expectancy, model life tables must be used to understand this population's age demography. These models, based on historical data, describe typical populations at different levels of mortality. For his demographic synopsis of the Roman Empire, Frier used the Model West framework, which he sees as "the most generalized and widely applicable." Because it is based on only one empirical input, the model life table can provide only a very approximate picture of Roman demography. On two important points, the table may seriously misrepresent the Roman situation: the structural relationship between juvenile and adult mortality, and relative mortality rates between men and women. In any case, Roman mortality should be expected to have varied greatly across time, place, and perhaps class. A variation of 10 years would not have been unusual. A life expectancy range of 20–30 years is therefore plausible, although it may have been exceeded in either direction in marginal regions (e.g. malarious urban districts on one end and high-altitude, low-density settlements on the other).
Model West, Level 3: A possible life table for the Roman Empire Females Males Age Mortality Cohort Life expectancy Mortality Cohort Life expectancy 0 0.3056 100,000 25.0 0.3517 100,000 22.8 1 0.2158 69,444 34.9 0.2147 64,826 34.1 5 0.0606 54,456 40.1 0.0563 50,906 39.0 10 0.0474 51,156 37.5 0.0404 48,041 36.2 15 0.0615 48,732 34.2 0.0547 46,099 32.620 0.0766 45,734 31.3 0.0775 43,579 29.4 25 0.0857 42,231 28.7 0.0868 40,201 26.6 30 0.0965 38,614 26.1 0.1002 36,713 23.9 35 0.1054 34,886 23.7 0.1168 33,035 21.3 40 0.1123 31,208 21.1 0.1397 29,177 18.7 45 0.1197 27,705 18.5 0.1597 25,101 16.4 50 0.1529 24,389 15.6 0.1981 21,092 14.0 55 0.1912 20,661 13.0 0.2354 16,915 11.8 60 0.2715 16,712 10.4 0.3091 12,932 9.6 65 0.3484 12,175 8.4 0.3921 8,936 7.7 70 0.4713 7,934 6.5 0.5040 5,432 6.1 75 0.6081 4,194 4.9 0.6495 2,694 4.6 80 0.7349 1,644 3.6 0.7623 944 3.4 85 0.8650 436 2.5 0.8814 225 2.4 90 0.9513 59 1.8 0.9578 27 1.7 95 1.0000 3 1.2 1.0000 1 1.2 After Frier, "Demography", 789, table 1. The specifics of any ancient age distribution would have seen heavy variation under local conditions. Moreover, the major cause of death in pre-modern societies was not the chronic, end-of-life conditions that characterize mortality in industrialized societies, or primary malnutrition. Instead, it was acute infectious disease, which has varied effects on age distributions in populations. For example, pulmonary tuberculosis characterized much of the Roman region in antiquity; the deaths it caused tend to be concentrated in the early 20s, where model life tables show a mortality trough. Similarly, in pre-modern societies for which evidence is available (e.g., Early Modern England, early–18th-century China), infant mortality varies independently of adult mortality to the extent that equal life expectancies at age 20 can be obtained in societies with infant mortality rates of 15–35%. Life table models, which assume that age-specific mortality ratios co-vary in uniform, predictable ratios, do not account for this fact. No ancient evidence can gauge this effect (the sources have a strong tendency to overlook infant death), and the model life tables might overstate it; comparative evidence suggests that it is very high and that mortality was strongly concentrated in the first years of life.
Mortality on this scale discourages investment in human capital, which hinders productivity growth, creates large numbers of dependent widows and orphans, and hinders long-term economic planning. With the prevalence of debilitating diseases, the number of effective working years was even worse: health-adjusted life expectancy (HALE), the number of years lived in good health, varies from life expectancy by no more than 8% in modern societies. In high-mortality societies, such as Rome, it could be as much as one sixth (17%) beneath total life expectancy. Adolescent mortality rates in Rome were two thirds higher than in early modern Britain. A HALE of less than 20 years would have left the Empire with very depressed levels of economic productivity.
Fertility
To maintain replacement levels under such a mortality regime—much less to achieve sustained growth—fertility figures needed to be very high. With life expectancies of 20–30 years, women would have to give birth to between 4.5 and 6.5 children to maintain replacement levels. Given elevated levels of divorce, widowhood, and sterility, the birth rate would have needed to be higher than that baseline, at around 6–9 children per woman. Fertility could not long have either fallen below or outstripped replacement levels. A population that maintained an annual growth or decline of 0.7% would double or halve itself, respectively, every century. Such rates are feasible locally or over a short period of time, and deaths could consistently outstrip births during epidemics. In the long term, convergence to maintenance levels was the rule.
The surviving census returns from Roman Egypt show a population that had not yet undergone the fertility transition. Artificial fertility controls like contraception and abortion were not widely used to alter natural fecundity in the Roman period. Only family limitation, in which couples ceased procreating after they had attained an acceptable level of children, could have been widespread. There is no indication that even this limitation was widespread, and the recorded distribution shows no evidence of being governed by parity or maternal age.
Marital fertility in Roman Egypt(Annual births per thousand married women) Age Roman Egypt Natural fertility Attested rates Gompertz model 12–14 22 23 225 15–19 232 249 420 20–24 343 333 460 25–29 367 325 431 30–34 293 299 396 35–39 218 262 321 40–44 219 166 167 45–49 134 37 24 After Frier, "Natural fertility," 325, Table 1.