<i>Waiting for the rains</i> : An attempt to evaluate the efficiency of the large Roman cistern at Barbariga Stancija (Casematte, Istria, Croatia)

ABSTRACT Access to freshwater has always been a critical factor in sustaining human settlements, especially in regions with limited water resources. In the Mediterranean region, where dry summers and karst landscapes limit water availability, ancient societies developed advanced methods for collecting and storing rainwater. Among these, cisterns played an important role in securing drinking water supplies. Despite their historical importance, the efficiency of these installations remains less studied than that of monumental aqueducts. This study focuses on a large Roman cistern at Barbariga Stancija in south‐western Istria, Croatia, where rainwater harvesting was essential for sustaining local settlements and supporting intensive agricultural production. By integrating archaeological evidence, contemporary climatological analysis and paleoclimatic reconstructions, we have developed a quantitative model that simulates the performance of the cistern under varying rainfall conditions. The analysis uses high‐resolution meteorological data and Weibull distribution‐based simulations to estimate annual water storage capacity and variations in supply reliability. The study also assesses the maximum number of people the cistern could have supported, based on a reconstructed daily per capita water consumption rate. Our results suggest that under average rainfall conditions, the cistern could have reliably supported approximately 25–28 people throughout the year. However, seasonal variations in rainfall led to significant fluctuations in water availability, potentially leading to shortages during the dry summer months. Comparative analyses with other Roman cisterns in the Adriatic region provide a broader context for understanding the functionality and limitations of such storage systems within ancient water management strategies. This research not only enhances our understanding of local Roman hydraulic infrastructure but also contributes to broader discussions on sustainable water management in arid and semi‐arid climates. It highlights the need for interdisciplinary approaches that integrate archaeology, climatology and hydrological modelling to comprehensively assess ancient water supply mechanisms and their implications for modern water conservation strategies.