There are two different kinds of question which historians might wish to ask about the population of the Roman world: how large was it or any of its constituent parts? and what were the patterns and tendencies of birth rates and death rates? Four kinds of information are available to offer imperfect answers to the first question: census figures, mostly for the Roman republic and early empire, where they served for the levy and, originally, taxation; figures relating to the feeding of (part of) the population of the city of Rome; occasional references to the population of particular cities or areas, usually without any possibility of knowing on what they were based; and figures for the carrying capacity of different areas of the Roman world in the earliest periods for which reasonably reliable figures exist. Almost no information is available for the second question; and one has to try to find the best fit of such scraps as there are with the model life tables compiled in the modern period for a variety of populations at different stages of economic development.
The Roman census figures purport to give the adult male population from the early republic to the early empire. Leaving aside the problem of the reliability of the early figures, some scholars have argued that they give for the republic only the adult male population above the property qualification for military service, excluding proletarii. If the figures really were only of those eligible, however, it would be hard to see why the Romans ever had problems of recruitment to the legions. On the other hand, it has also been argued that the rise in the total under Augustus is so large that it can be explained only on the assumption that the figures now included women and children:This view is by no means universally accepted; and the alternative view argues that the difference is to be explained by the enfranchisement of Transpadane Gaul in 49 bc and by the greater efficiency of registration. In any case, the figure of 4,063,000 will have included large numbers of Romans living overseas, and comparisons with guesses as to the total (male) population of Italy in any earlier period are hazardous. Similarly, we cannot know how far rises in numbers after Augustus are due to manumissions of slaves (see slavery) and enfranchisements of provincials (see citizenship, roman).
There will always have been some under‐registration in the census, probably substantial after tributum ceased to be collected after 167. The rise in numbers between 131 and 125 is probably to be related to the agrarian law of Tiberius Sempronius Gracchus 2; but it is not clear whether it is due to recipients of plots of land bothering to register for the first time or to men registering in order to prove their eligibility. The relatively low rise in 86, after the enfranchisement of peninsular Italy in 90 is probably to be explained by the difficulty of conditions in the aftermath of the Social War.
All arguments about trends are made difficult by uncertainty over the scale of losses due to war casualties and the removal of Roman citizens to Latin colonies (see colonization, roman), and of additions to citizen numbers through the manumission of slaves and the incorporation of new citizens from other communities.
Subjects: Classical Studies.