Demography of the Roman Empire

The Roman Empire's population has been estimated at between 59 and 76 million in the 1st and 2nd centuries,^[1] 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,^[2] 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.^[3]

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.^[1]

Due to migration, the ethnic composition of the city of Rome, its vicinity, and Italy as a whole went through substantial change 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 medieval ages and the early modern period. The resultant changes are reflected in the differences between Northern and Southern Italy to this day.^[4] The genetic distance between Northern and Southern Italians, although large for a single European nationality, is similar to that between the Northern and the Southern Germans.^[5]

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 percent 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 percent per year.^[6] 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 percent annual growth (Europe as a whole saw 0.1 percent annual growth rates), and the north African and west Asian parts of the empire saw almost no growth at all.^[7]

By comparison, what is now the territory of China experienced 0.1 percent annual growth from 1 CE to 1800 CE. After a population decline following the disintegration of the western half of the Roman state in the 5th and 6th centuries, 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.^[7]

There are no reliable surviving records for the general demography of the Roman Empire. There are also no detailed local records, such as 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 comparison rather than records and observations.^[8]

Life expectancy at birth in the Roman Empire is estimated at about 22–33 years.^{[9][notes 1]} For the two-thirds to three-quarters of the population surviving the first year of life,^[10] 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.^[11] The ~50% that reached age 10 could expect to reach ~45–50,^[10] and the 46–49% surviving to their mid-teens could on average expect to reach around 48–54,^[11] although many lived much longer or shorter lives for varied reasons, including wars for males and childbirth for females. Even if these figures rely more on conjecture than ancient evidence, which is sparse and of dubious quality, the known social and economic 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.^[12]

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, which show life expectancies at birth of between 22 and 25 years, results broadly consistent with model life tables.^[13] 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, such as 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.^[14]

As no population for which accurate observations survive has 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".^[15] 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 the relative mortality rates across the sexes.^[16] In any case, Roman mortality should be expected to have varied greatly across times, places, and perhaps classes.^{[17][notes 2]} A variation of ten years would not have been unusual. A life expectancy range of between 20 and 30 years is therefore plausible,^[19] 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).^[14]

The specifics of any ancient age distribution would have seen heavy variation under the impact of local conditions.^[14] 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; its deaths tend to be concentrated in the early twenties, where model life tables show a mortality trough.^[20] Similarly, in pre-modern societies for which evidence is available, such as early modern England and early 18th-century China, infant mortality varies independently of adult mortality, to the extent that equal life expectancies at age twenty can be obtained in societies with infant mortality rates of 15% to 35% (life table models omit this; they depend on the assumption that age-specific mortality ratios co-vary in uniform, predictable ratios).^[21] 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.^[22]

Mortality on this scale discourages investment in human capital, which hinders productivity growth (adolescent mortality rates in Rome were two-thirds higher than in early modern Britain), 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. A HALE of less than 20 years would have left the empire with very depressed levels of economic productivity.^[23]

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 twenty to thirty, 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 to 9 children per woman.^[24] Fertility could not long have either fallen below or outstripped replacement levels. A population which maintained an annual growth or decline of 0.7% would double or halve itself 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.^[25]

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.^[26] 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.^[27]

Imperial Rome largely conforms to what is known as the Mediterranean pattern of marital fertility: men married late and women married early.^[29] The evidence on marriage age is fairly robust for Roman elites: men in the senatorial class were expected to marry in their early twenties, while women were expected to marry in their early teens. According to the most plausible interpretation of the evidence from funerary commemoration among the lower classes, women married in their late teens or early twenties, and men married in their late twenties or early thirties.^[30]

The Roman pattern thus stands in contrast to the Eastern (i.e. East Asian) pattern, in which both men and women married young.^[29] China, the major example of the Eastern pattern, also had lower levels of fertility than Rome. This was apparently achieved by a combination of prolonged breastfeeding, selective female infanticide, and male celibacy, although the details are controversial.^[31] Roman families share some features of the Eastern pattern. For example, Roman Egypt had a custom of extended breastfeeding, which may have lengthened birth spacing. Egyptian fertility levels are comparable to those recorded in the early modern Japanese village Nakahara, where about half the population practiced family limitation. On the historian Walter Scheidel's judgment, this speaks to the incidence of family limitation even in what are supposedly natural fertility regimes.^[32]

Roman and Greek literary and legal tradition makes frequent reference to the Eastern demographic features of infanticide and child exposure. Although the extent of these practices is unlikely to have been small, it is nonetheless impossible to quantify, and reported gender ratios do not permit judgment on the prevalence of femicide. These Eastern features did not prevail in medieval or modern Europe, where there were cultural and structural factors directly discouraging them or diminishing their effects on childhood mortality; these included among others religious doctrine, legal enforcement, institutions of foundling care, child labor, and wet-nursing. These constraints were weak or absent in Greek and Roman society.^[33]

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Genetic studies have indicated that the Iron Age population of Latium was a mixture of preceding Early European Farmers and Western Hunter-Gatherers, with about 30% Steppe ancestry largely coming from the Pontic–Caspian Steppe. However two out of six individuals from Latin burials from Latium vetus were found to be a mixture of local Iron Age ancestry and an ancient Near Eastern population (best approximated by Bronze Age Armenian or Iron Age Anatolian population). In addition, one out of four individuals from Etruscan civilization burials from Veio and Civitavecchia, a female, was found to be a mixture of local Iron Age ancestry and a North African population (best approximated by Late Neolithic Moroccan).^[34][35]

The results have indicated a substantial migration from the Eastern Mediterranean into the city of Rome and its vicinity in Central Italy during the Principate. Notably, only 2 out of 48 Imperial-era individuals fall in the Spanish-like cluster to which 8 out of 11 Iron Age individuals belong.^[34] Instead, two-thirds of Imperial individuals (31 out of 48) overlap with central and eastern Mediterranean populations, such as those from southern and central Italy, Greece, Cyprus, and Malta. An additional quarter (13 out of 48) of the sampled Imperial Romans overlap with Levantine and Near Eastern populations, projecting close to four contemporaneous individuals from Lebanon.^[34][35]

One study indicates that during Late Antiquity this Eastern Mediterranean migration subsides and is replaced by the migration of northern barbarian European nations. Consequently, the ethnic composition begins to take an increasingly European character, a trend that intensifies during the Migration Period and continues even long after the collapse of the Western Roman Empire, as the geopolitics of Italy tie it ever more with its northern neighbors, e.g. via the Holy Roman Empire.^[34] These contrasting migratory waves may have contributed to the modern genetic differentiation along the length of the Italian peninsula, with the contrasting Spanish-like Northern Italy, and Greek-like Southern Italy.^[35] The authors^[who?] suggest that this has also been contributed by Arab conquests, especially via the Emirate of Sicily, after Western Rome had already fallen.^[36] This is unlikely^{[citation needed]}, considering that only 0.6% of modern Southern Italians have the typical Maghrebin core haplotype. Overall, the estimated Central Balkan and North Western European paternal contributions in South Italy and Sicily are about 63% and 26%, respectively.^[37]

Tenney Frank published in 1916 an analysis of the names in inscriptions on graves, tombs and in columbaria holding cremated remains. He reported that while foreign migration was greatest into the city of Rome itself, the native populations may have been reduced to a minority throughout all of Italy.^[38] Additionally, he suggested that this migration was primarily based on slave importation and not free immigrants, and that due to large numbers of slaves being freed and their higher fertility, in contrast to "race suicide" among the more sophisticated citizens, slaves and their descendants came to comprise many or most of the population. He asserted that "what lay behind and constantly reacted upon [the] causes of Rome's disintegration was, after all, to a considerable extent, the fact that the people who built Rome had given way to a different race".^[38]

There are not many contemporary statements about migration into Italy and Rome. Of the statements that have survived, most are either cautious or negative towards the inflow of foreigners, and may indicate the wide extent to which it occurred. For example, the historian Suetonius records two notable cases where policies had been undertaken to assuage the tensions arising out of the mass importation of slaves. In the first case, the dictator for life Julius Caesar had decreed a requirement that at least one third of the workforce employed in herding be freeborn as opposed to slaves — herding being one of the main labors in Italy. In the second case, the first emperor Octavian–Augustus goes further and seeks to limit the granting of freedom and citizenship to slaves altogether.^{[39][notes 5]} This tension between the native population and a foreign inflow during the empire is also reflected in a private letter from Seneca the Younger to his mother.^{[39][notes 6]}

In the social commentary of the satirist and poet Juvenal, he laments repeatedly in Satires of the inflow of foreign Greeks into Rome, and of the encroachment of their traditions.^{[notes 7]} While the satirical character of the writing necessitates caution, the fifth line referring to the Orontes river in Syria has been proposed to refer to the Syrian origin of most of the imported slaves, with Eastern slaves traditionally bearing Greek names.^[38] Coincidentally, 21st-century genetic studies have lent credibility to this interpretation. Some of the contemporary statements offer light on the wide extent of foreigners in ancient Rome, especially in the form of slaves. For example, the prevalence of freedmen (ex-slaves) is commented on by the historian Tacitus, who wrote: "If freedmen were to be a separate class, the paucity of the freeborn would be conspicuously apparent."^[41] In a similar vein, in a speech to voters in Rome, Scipio Aemilianus had reminded the voters how he had brought a large part of them to Rome as captives, indicating to what extent previous war captives from Africa or Spain may have comprised the commoner population at the time, right after the Third Punic War.^[42] While most of these statements are cautious or negative towards foreigners, a speech by the emperor Claudius, called the Lyon speech (after the location where the tablet originated), offers a more positive attitude towards provincials foreign to Italy; he successfully urges senators to accept rich Gauls from Lugdunum into the Roman Senate, by praising their loyalty and devotion to Rome.^[43]

The geography of the Mediterranean made it fairly convenient for local migration to occur from village to village — especially as the successful dedication and expansion of new settlements required it.^[44] Numerous times this was also applied for the establishment of colonies outside of Italy; at the beginning of the empire, about 750,000 Italians lived in the provinces.^[45] Julius Caesar, Mark Antony, and Augustus settled many of their veterans in colonies, in Italy, and the provinces. Those established in Italy up to 14 BCE have been studied by Keppie 1983. In his account of the achievements of his long reign (Res Gestae), Augustus stated that he had settled 120,000 soldiers in twenty colonies in Italy in 31 BCE, then 100,000 men in colonies in Spain and southern Gaul in 14 BCE, followed by another 96,000 in 2 BCE.^[46] Historian Brian Campbell also states that "[f]rom 49 to 32 BCE about 420,000 Italians were recruited" — which would thus be the veteran (citizen) stock that was largely sent to the provinces (colonies) during Augustus; the Lex Calpurnia also allowed citizenship to be granted for distinguished bravery, such as with the 1,000 Socii from Camerinum after the Battle of Vercellae 101 BCE (Plutarch Mar. XXXVIII) or the auxiliary (later Legio XXII Deiotariana) after the Battle of Zela. By the time of Augustus, the legions consisted mostly of ethnic Latins/Italics and Cisalpine Gauls.^[47] Historian Theodore Mommsen estimated that under Hadrian nearly one third of the eastern Numidia population (roughly modern Tunisia) was descended from Roman veterans.^[48]

Modern estimates of the population of the Roman Empire started with the fundamental work of 19th-century historian Karl Julius Beloch.^[49] His estimates of the area of different components of the empire, based on planimetric estimates by contemporary military cartographers, have not been challenged by any more modern analyst. By providing a check to population densities, these area figures compel a baseline level of plausibility.^[50] Beloch's 1886 estimate of the population of the empire in 14 CE has withstood contemporary and 21st-century criticism, and underlies modern analysis (his 1899 revision of those figures is less esteemed). Only his estimates for Anatolia and Greater Syria required extensive revision; Beloch's estimated population figure, 19 million, produced population densities not otherwise achieved in those areas until the 20th century. In a 2000 estimate of the population of the empire, Frier suggested a figure of 12 million as "considerably more plausible".^[51] Beloch's figures for Spain and Africa have also been revised downwards.^[51] In a 2017 publication, historian Kyle Harper suggests 75 million for the empire as a whole with 16 million for Anatolia and Greater Syria.^[2] This estimate produces a population density of about 20 inhabitants per square kilometer, which is a low figure by modern standards (for example, among countries and dependencies by population density, the United Kingdom has a density of well over 200/km²). The population density in the Greek East was 24/km², denser than the Latin West at 17/km²; only the Western provinces of Italy and Sicily had a density higher than the average of the East.^[2]

Harper estimates the population at the time of Augustus at 60 million, a ninth more than Beloch's 1886 estimate, and suggests a population growth rate of 0.1% per year, reaching 75 million after nearly two centuries of growth.^[2] Early 21st-century estimates suggest that slaves constituted about 15 percent of the Empire's total population; the proportionate figure would be much higher in Italy and much lower in Africa and Egypt.^[53] Frier's estimate produces a population density of 13.6 inhabitants per square kilometer. The population density in the Greek East was 20.9/km², twice as dense as the Latin West at 10.6/km²; only the Western provinces of Italy and Sicily had a density comparable to the East.^[54]

There are few recorded population numbers for the whole of antiquity, and those that exist are often rhetorical or symbolic. Unlike modern nations, Roman citizenship was not granted automatically to inhabitants of Roman territory outside of the city of Rome and its hinterlands. By the 1st century BCE, citizenship was extended to the whole of the Italian peninsula, a region that only constituted 5% of the territory of the Roman Empire. In addition, Roman censuses only measured their adult citizen population, and it is unclear if and when women were counted as citizens as well. Most surviving Roman census return figures date from the late period of the Roman Republic and the Early Empire. Serial statistics for Roman citizen numbers, taken from census returns, survive for the early Republic through the 1st century CE.^[56] Only the figures for periods after the mid-3rd century BCE are reliable. Fourteen figures are available for the 2nd century BCE (from 258,318 to 394,736). Only four figures are available for the 1st century BCE, and exhibit a large break between 70/69 BCE (910,000) and 28 BCE (4,063,000). The interpretation of the later figures—the Augustan censuses of 28 BCE, 8 BCE, and 14 CE—is therefore controversial.^[57] Alternate interpretations of the Augustan censuses, such as those of historian Elio Lo Cascio,^[58] produce divergent population histories across the whole imperial period.^[59]

The enfranchisement of the Cisalpine provinces and the Italian Allies after the Social War would account for some of the population growth of the 1st century BCE.^[57] Alternate readings of the Augustan census both accept the basic accuracy of the figures; they assume different methods on the part of the census-takers. The standard interpretation assumes that the census-takers included all citizens—men, women, and children—in the Augustan censuses; the revised interpretation assumes that the census-takers only counted adult men, as they had during the Republican period. While the standard interpretation is not supported by any evidence internal to the text, it reduces the implied population totals for Italy in 28 BCE from 10 million to a more plausible 4 million.^[57] The high total earns support from recorded conflict over land in the late Republic and other indications of population pressure; at the same time, it does not accord well with comparative evidence from other periods and other parts of the empire.^[60]

Beloch's 1886 estimate for the population of the empire during the reign of Augustus was as follows:^[61]

The historian J. C. Russell's 1958 estimate for the population of the empire in 350 CE was as follows:^[62]

Demographic studies have argued for a population peak ranging from 70 million (comparable to the contemporaneous and similarly sized Han empire in China), with one-tenth of them located in Italy itself, to more than 100 million.^[63]

By the standards of pre-modern economies, the Roman Empire was highly urbanized. As of 2016, 1,388 urban sites had been identified in the Roman world dating from the late Republican and early Imperial periods.^[64] At its peak, the city of Rome is widely thought to have contained at least a million inhabitants, a total not equaled again in Europe until the 19th century.^[65] As the imperial capital, Rome was sustained by transfers in kind from throughout the empire; no other city could be sustained at this level. The other major cities in the empire, such as Alexandria, Antioch, Carthage, Ephesus, and Salona, had populations of over a hundred thousand, with Alexandria having a population estimated at half a million.^[65]

Most of these 1,388 cities were small, usually possessing around 5,000 inhabitants. Of the 885 cities whose built-up area has been estimated, 405 cities (slightly less than half) have an area that suggests a population larger than 5,000 and approximately 8% (69 out of 885) of the sites have an area suggesting a population larger than 30,000. Extrapolation from a sample of 52 excavated sites has suggested an imperial urban population of 14 million in around 600 cities with over 5,000 inhabitants, a quarter or a fifth of modern estimates of the Empire's total population, a higher proportion than in Europe at the turn of the 19th century.^[65]

High mortality rates and pre-modern sanitary conditions made urban regions net population sinks, with more local deaths than births. They could only be sustained by constant immigration.^[66] The large cities provided a major stimulus to demand, and not only for agricultural products but for manufactured goods and luxury items as well.^[67]

In 1958, Russell produced estimates for the urban population in Late Antiquity. These estimates, which are much lower than 21st-century estimates that refer to the Early Imperial period, are as follows:^[62]

• Classical demography
• Demographic history

• Bondioli, Luca; Garnsey, Peter; Knyf, Martin; MacChiarelli, Roberto; Prowse, Tracy L.; Schwarcz, Henry P. (2007). "Isotopic Evidence for Age-Related Immigration to Imperial Rome". American Journal of Physical Anthropology. 132 (4): 510–519. doi:10.1002/ajpa.20541. PMID 17205550.
• Killgrove, Kristina; Montgomery, Janet (2016). "All Roads Lead to Rome: Exploring Human Migration to the Eternal City through Biochemistry of Skeletons from Two Imperial-Era Cemeteries (1st–3rd c AD)". PLOS ONE. 11 (2): e0147585. Bibcode:2016PLoSO..1147585K. doi:10.1371/journal.pone.0147585. PMC 4749291. PMID 26863610.