Researchers from the Weizmann Institute and the Israel Antiquities Authority have dated the Siloam Pool Dam to the late ninth century BCE. In a commentary article in PNAS, Prof. Guy Bar-Oz and Prof. Gideon Avni of the University of Haifa emphasize the importance of urban water security – then as now.
Jerusalem Day, which took place last week, is an opportunity to look not only at the city of today, but also at the challenges that ancient Jerusalem faced. One of the main challenges was water supply. Research by the Weizmann Institute of Science’s Scientific Archaeology Unit, in collaboration with the Israel Antiquities Authority, has dated the monumental dam of the Pool of Siloam to 805–795 BCE. The study was published in the Proceedings of the National Academy of Sciences, PNAS.
The original study was led by Dr. Johanna Regev and Prof. Elisabetta Boarto of the Weizmann Institute, in collaboration with archaeologists Dr. Nachshon Zenton, Dr. Philip Vukosbovich, and Itamar Barko of the Israel Antiquities Authority. The researchers used microarchaeological methods and carbon-14 dating of tiny organic materials trapped in the dam’s mud during its construction, including microscopic straw and charred branches. According to the Weizmann Institute, the precise dating range is an exceptional achievement for an archaeological find that is more than 2,800 years old.
Following the study, Prof. Guy Bar-Oz and Prof. Gideon Avni, from the School of Archaeology and Maritime Civilizations at the University of Haifa, wrote a commentary article in PNAS. Their article is not the research itself, but a broader discussion of the significance of the finding for understanding urban water security in Jerusalem and other ancient cities. According to PubMed, their article was published in September 2025 as a response or commentary to a study on the dating of the Siloam Dam. (PubMed)
A water system for a city without a river
Ancient Jerusalem was a mountainous city without a major river. It relied on local water sources, most notably the Gihon Spring. Such sources are sensitive to changes in rainfall. When a series of dry years reduces the flow of springs, even a well-established city can run into water shortages.
According to a statement from the Weizmann Institute, the researchers combined the dam's dating with climate data from Sorek Cave, drilling in the Dead Sea, and indicators related to solar activity. This combination led them to conclude that the dam was part of a broader water system designed to cope with challenging climatic conditions: dry years alongside short, heavy rain events that could cause flash floods.
The Weizmann Institute said that “the findings indicate extensive urban planning for managing Jerusalem’s water system as early as the ninth century BCE.” The researchers saw this as evidence of the city’s ability to carry out a major engineering project during the period of the Kingdom of Judah.
Water security since ancient times
According to Prof. Bar-Oz, the case of Jerusalem illustrates that water crises are not a new phenomenon. In the past, cities have had to deal with droughts, declining water availability, and rapid environmental changes. In the case of Jerusalem, the response was to build a large-scale storage system, designed to store water for dry seasons and improve the city's resilience.
The key point, according to Bar-Oz and Avni, is that the dam and the Siloam Pool are not just impressive archaeological remains. They teach about early urban thinking: how a city plans its future in the face of climatic uncertainty. In other words, as early as 2,800 years ago, water security was part of a city’s ability to grow, function, and survive.
A lesson from the past for the present
Comparisons to today should be made with caution. Ancient Jerusalem is not like modern cities, and the tools available to its residents were completely different. In the past, water solutions relied on dams, ponds, canals, and aqueducts. Today, this has been supplemented by seawater desalination, wastewater recycling, advanced monitoring, and regional management of water resources.
Still, the basic principle is the same. A city that does not guarantee itself a reliable water supply will struggle to maintain its resilience. The study of the Siloam Dam reminds us that dealing with water shortages has accompanied cities throughout history, and that water crises have been a central factor in shaping urban, economic, and social systems.
In this sense, the study of ancient Jerusalem is not just a look into the past. It provides an important point of comparison for questions that cities still face today: how to prepare for changing droughts, how to manage limited water resources, and how to build urban systems that can withstand climate change.
Short FAQ
Who conducted the original research?
The original study was conducted by researchers from the Weizmann Institute of Science in collaboration with the Israel Antiquities Authority, and was published in PNAS.
What was discovered about the dam?
The Siloam Pool Dam has been dated to 805–795 BCE, using carbon-14 dating of organic materials trapped in the construction mortar.
Why is the finding important?
It indicates advanced urban planning of a water system in Jerusalem as early as the ninth century BCE, probably against a backdrop of challenging climatic conditions. According to the researchers, the dam was intended to help store water and cope with declining precipitation and flash floods.
What does that have to do with today?
The finding shows that urban water security was a major challenge in ancient cities. Even today, cities are required to plan for the long term in the face of droughts, pressure on water resources, and climate change.
More of the topic in Hayadan:
