New Insights Into Early Islamic Hydro-Agricultural Strategies in Northwest Arabia: A Geoarchaeological Study of al-Bint Dam (Sadd al-Bint)

Abstract

The Sadd al-Bint is one of the largest known ancient dams in Saudi Arabia, and yet, its construction date, function and collapse remained uncertain. This study presents the first numerical chronology for the dam, integrating radiocarbon dating, Bayesian modelling, geomorphological analysis and hydrological modelling to reconstruct its history. Results indicate a multiphase construction, with initial building between 596 and 686 CE, followed by repairs or extensions between 725 and 907 CE, and a final maintenance phase between 947 and 1015 CE. Structural and sedimentological evidence suggests that the dam's collapse was not due to poor engineering but rather prolonged lack of maintenance, leading to progressive infiltration until a sudden hydrological event triggered failure. Hydrological reconstructions confirm a maximum reservoir capacity of 12 million m³, potentially supporting extensive irrigation at nearby al-Thamad oasis. The study brings new insights on the dating of Arabian dams, perhaps its most challenging issue, demonstrating a major hydraulic investment during the Rashidun and Umayyad periods and its continuity into the Abbasid period. The dam's strategic location and its role in regional water management suggest a broader state-driven infrastructure policy in early Islamic Arabia. These findings enhance our understanding of long-term water management strategies in northwestern Arabia and their socio-political implications.