[T]he only countries that come close to the likely life expectancy of the average Roman are a long list of terribly poor countries, all but Afghanistan located in sub-Saharan Africa, most with very high levels of HIV infection in addition to any number of other illnesses. But even the worst-off country, Swaziland, comes at 39.6 years at least a decade ahead of the Roman average and on par with the luckiest Roman districts.
Combine this with the very high disease load of the average Roman and sustained undernourishment . . . at least as measured by average height, the food supply improved after the Roman Empire's collapse in the west--and the picture of a congenitally unhealthy population is inescapable. Combine that with the abundant evidence for the exceptionally unequal distribution of wealth and power within the Roman Empire, and with the significantly lower level of economic output (estimated . . . to be inferior to that of central Africa and, of course, lacking the imported technologies available to central Africans) and you have a Rome that stands few comparison with even the worst-off countries of our 21st century world. . . .
In pre-modern societies, the major cause of death was not the chronic, end-of-life conditions that characterize mortality in industrialized societies, nor primary malnutrition, but acute infectious disease, which has varied effects on age distributions in populations. Pulmonary tuberculosis, for example, characterized much of the Roman region in antiquity; its deaths tend to be concentrated in the early twenties, where . . . [data] show a mortality trough. Similarly, in pre-modern societies for which evidence is available, such as early modern England and early eighteenth-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%.
The oldest Romans were as old as elderly people today, or close, but they were rare.
Little wonder, then, that life was cheap then.