As a pre-transition society, Rome undoubtedly had far higher birth and death rates than those of the industrialized world today: more than 35 births and deaths per 1,000 per year, as compared with less than 10 births and deaths per 1,000 today. The aim of this chapter is to review and evaluate the problematic evidence and arguments for mortality and fertility rates and ages at marriage in the Roman population, and thus to justify the choices for the values of the parameters used in the microsimulation.

Mortality

The mortality experience of a population can be expressed in various ways. Most directly, the mortality rate can be summarized as the number of deaths per thousand per year – a statistic of interest to the historian studying broad trends in the population as a whole. For the historian concerned with the individual and family experience, it is more useful to think in terms of mortality rates at given ages, from which average life expectancy (e) may be derived. Average life expectancy is the average number of years those of a particular age will live and is calculated by adding together the additional years of life of those of a given age and then dividing by the number of individuals in that age group. It is important to keep in mind that average life expectancy is not the typical, or modal, experience. In a population with an average life expectancy at birth of twenty-five (eo = 25), the most common age at death will be under one year and relatively few will die at age twenty-five.