High-resolution isotopic data link settlement complexification to infant diets within the Roman Empire

Our study explores the potential relationship between infant feeding practices and settlement complexity in the Roman Empire through high-resolution Bayesian-modeled stable isotope measurements from incremental dentine. We compiled isotopic data from permanent first molars of individuals from various Roman sites: five from Bainesse (UK), 30 from Thessaloniki (Greece), along with new carbon and nitrogen isotope analyses from four individuals from Pompeii and six from Ostia Via del Mare (AVM). Our results reveal significant inter-site variability in breastfeeding durations, ranging from 1.5 years to approximately 5 years. Notably, individuals from the highly complex urban centers of Pompeii and Thessaloniki ceased breastfeeding around or below the 2-year weaning threshold recommended by Roman physicians. In contrast, individuals from the rural site of Ostia AVM and the site of Bainesse, near the northern frontier of the Roman Empire, generally ceased breastfeeding after 2 years of age. The link between settlement complexity and duration of breastfeeding observed in our study may have resulted from adherence to medical guidelines, support infrastructures, and/or strategies to mitigate financial constraints within households.