A massive dam dating back nearly 2,800 years has been uncovered at the Pool of Siloam, offering rare insight into urban planning during the First Temple period in ancient Jerusalem.
The structure, linked to efforts by the kings of Judah to manage extreme weather, is now considered a key part of one of the earliest known city-wide water systems. Researchers believe this First Temple dam, discovered in Jerusalem’s City of David, was built between 805 and 795 BCE.
The Israel Antiquities Authority and the Weizmann Institute of Science made the discovery. Their findings suggest the dam was constructed in response to a severe climate crisis, a troubling mix of limited rainfall with sudden, intense storms.
The structure stood about 12 meters (39 feet) high, over 8 meters (26 feet) wide, and extended 21 meters (69 feet) long—designed to contain runoff from both the Tyropoeon Valley and the Gihon Spring, two major water sources in the region.
Unified water system from the ninth century BCE
The dam formed part of an advanced water management system that included a tower blocking the Gihon Spring and a large reservoir. Water collected at the spring was funneled through a channel into the Siloam Pool, which also received floodwater held back by the dam.
By the end of the ninth century BCE, these three elements worked together as a single hydraulic system, built to safeguard the growing city from both drought and flash floods.
Researchers dated the construction using carbon-14 analysis of wood and plant remains found in the dam’s mortar.
Dr. Johanna Regev and Prof. Elisabetta Boaretto of the Weizmann Institute said the materials provided a precise date, narrowing the timeframe to a 10-year window at the end of the ninth century BCE—a rare level of accuracy in archaeological studies.
High-precision dating confirms biblical links
The research, published in the Proceedings of the National Academy of Sciences of the United States of America, will also be presented at the City of David Research Conference in early September. The event will be called “The Lost Pool – The Mystery of the Siloam.”
Excavation director Dr. Nahshon Szanton noted that the project likely influenced ancient Jerusalem’s expansion, especially toward Mount Zion, where residents relied on water from the Siloam Pool.
Dig manager Itamar Barko added that the dating evidence confirms the dam served as the foundation for the pool, which is mentioned in biblical texts.
Israel Antiquities Authority director Eli Escusido described the structure as one of the most significant and best-preserved engineering achievements from the First Temple era.
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