For many Romans, life was short. In consequence, the young greatly outnumbered the elderly. Historians have long accepted these basic truths, even if they are only beginning to come to terms with the social implications of an alien demographic regime. But how short is ‘short’, and how many Romans were children, how many adults? Does it matter, and can we know?
The importance of demographic structure is not in doubt. High mortality causes scarce energy resources to be wasted in pregnancies and nursing, and poses a disincentive to investment in education. It destabilizes families and households, exposes orphans and widows to risk and potential hardship, and shortens the time-horizons of economic activity. In the long term, average life expectancy is the principal determinant of fertility. Poor chances of survival trigger high birth rates to ensure genetic survival. High fertility, in turn, is negatively correlated with the status and well-being of women, and constrains female participation in economic and public affairs. Overall age structure, in conjunction with cultural practices from marriage to child care, determines the prevalence of orphans and widows, and affects the age-specific distribution of fertility. In sum, age structure is instrumental in framing and shaping expectations and experiences. For this reason alone, our understanding of life in the Roman world is critically dependent on our knowledge of demographic conditions.