Radiocarbon analysis has revealed that Jerusalem’s Siloam Dam was constructed around 800 BCE, offering new insight into how ancient Jerusalem responded to extreme climate conditions. The structure, part of a broader water management system, was likely a response to recurring droughts and sudden flash floods that threatened the city’s water supply more than 2,800 years ago.
A recent study by the Weizmann Institute of Science and the Israel Antiquities Authority confirms that the massive dam was built between 805 and 795 BCE. Researchers say the project likely took place under the rule of King Jehoash or his successor, Amaziah, during a time when water security was a pressing concern.
The dam was designed to secure and redirect water from the Gihon Spring into the Siloam Pool, an artificial reservoir that also collected rainwater. By doing so, city leaders created a controlled and reliable water source for residents in an era of unpredictable weather.
Precise dating through advanced methods
The research was published in the Proceedings of the National Academy of Sciences. The team, led by Dr. Johanna Regev and Prof. Elisabetta Boaretto of the Weizmann Institute, worked with archaeologists Dr. Nahshon Szanton, Dr. Filip Vukosavović and Itamar Berko of the Israel Antiquities Authority.
To determine the dam’s age, researchers applied microarchaeological techniques and radiocarbon dating to organic materials trapped in the construction mortar. These included charred twigs and microscopic straw fragments that had remained undisturbed since the dam was first built. The tight dating range—just a decade—marks a rare achievement in archaeological studies of ancient architecture.
The team also linked their findings to environmental data to better understand the conditions of the time. Using climate records from Dead Sea sediment cores, Soreq Cave stalagmites, and solar activity indicators, researchers painted a detailed picture of the 9th-century BCE climate. The correlation between the dam’s construction and documented climate stress supports the idea that the structure was a strategic response to environmental challenges.
A symbol of strategy and resilience
According to the researchers, the scale and planning of the dam point to significant political organization and technical capability. Boaretto and Regev note that this kind of infrastructure shows Jerusalem was not only expanding but also adapting to major environmental pressures.
Their findings indicate that Jerusalem’s Siloam Dam was more than a water source—it was a long-term solution to a growing climate crisis and a symbol of the city’s resilience.
