Climate Variability, Grain Supply, and Food Security in Ancient Rome

Abstract. The Roman world has become a central case in debates on past climate–society interactions, particularly regarding the empire's expansion, transformation, and decline. However, despite growing recognition that these interactions were mediated through complex socio-economic and ecological processes, the mechanisms through which climatic variability translates into historical outcomes are rarely investigated explicitly. In this paper, we investigate whether climatic variability was systematically associated with historically attested food shortages in ancient Rome, explicitly accounting for changes in the geographical configuration of the city's provisioning system. Combining annual palaeoclimatic reconstructions from climate field reconstructions (PHYDA and GEDA) with a dataset of 55 attested shortage events for the period 1–650 CE, we analyse temperature and hydroclimatic variability across Rome’s principal grain-supplying regions. The analysis combines probit regression models with Monte Carlo simulations to test associations with both short-term climatic shocks and sustained climatic anomalies. The results provide no evidence for a stable, system-wide climate–shortage relationship. Throughout the Imperial and Late Antique periods, statistical associations are weak and regionally variable, suggesting a provisioning system that buffered regional climatic variability. A clearer, albeit modest, climatic signal emerges only after the contraction of Rome’s supply network in the late fifth century CE. Overall, the findings indicate that, based on historically attested food shortages, climatic variability influenced Rome's food security not as a direct or uniform trigger, but as a conditional stressor whose effects depended on the changing structure of Rome's provisioning system.