Biblical kings in Jerusalem built monumental dam, maybe to deal with climate change (2025)

In the jumble of superimposed ruins from different periods that lies at the heart of ancient Jerusalem, one structure has been popping up in archaeologists' reports for more than a century. It's a massive wall, identified as a dam that lined the Pool of Siloam, a key element of the city's ancient water system and a site at the center of multiple biblical passages.

Now, archaeologists digging in the heart of the contested neighborhood of Silwan in East Jerusalem have extensively excavated this enigmatic structure and, for the first time, radiocarbon experts have been able to figure out when it was built.

The results are surprising, showing that the dam was older than previously thought and was built in the early days of the Kingdom of Judah, roughly around 800 B.C.E., the experts reported Monday in PNAS.

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The dam is only the latest in a slew of recent discoveries in Jerusalem that can be linked to this part of the First Temple Period, and attest to a time of early expansion of the city at the turn of the 9th-8th century B.C.E., possibly under the rule of King Jehoash. Specifically, the construction of the dam may have been triggered by a greater need to store and control Jerusalem's key water supply in a time of climate change that brought longer dry periods, the researchers speculate.

The Siloam Pool is located in the Palestinian neighborhood of Silwan, also dubbed the "City of David" because it hosts the oldest ruins found so far in Jerusalem and is therefore believed to have been a core part of the settlement pretty much since Canaanite times.

The pool, also known as Birket el-Hamra in Arabic (named for red clay), is located at the end of ancient underground rock-cut channels that brought the waters of the Gihon Spring, Jerusalem's only perennial water source, safely into the walls of the City of David. One such pool and channel are mentioned in the Bible (2 Kings 20:20) as having been built by King Hezekiah around 700 B.C.E. in preparation for an Assyrian siege.

Much later, in the Roman period, the Siloam Pool was lined with a monumental stone staircase, and became the setting for the story of Jesus (John 9:1-12) healing a blind man.

The dam that hemmed in the pool's waters has attracted less attention, although it has been partially excavated at different times since the late 19th century, explains Dr. Nahshon Szanton, an archaeologist with the Israel Antiquities Authority who leads the latest dig at the Siloam Pool.

Between 2023 and 2024 Israeli archaeologists excavated the entirety of the pool site as part of efforts to develop the site for tourism. The dig has not been without controversy, seeing as it was carried out in one of the most volatile neighborhoods of East Jerusalem, on land previously cultivated by Palestinian residents as an orchard, and financed by Elad, a right-wing NGO that promotes Jewish settlement in Silwan.

Straw argument

The results of the dig are certainly notable in revealing an unknown side of the city's history. The archaeologists fully unearthed the ancient dam, realizing for the first time its monumental size and technical complexity, Szanton says. The structure was at least 19 meters long, 11 meters high, and 10 meters wide, the archaeologists report. It included both sheer vertical and slanted sections, in order for the wall to resist the pressure of the water it was holding, he says.

But inquisitive minds wanted to know when and why it was built. Previous expeditions that partially unearthed the wall suggested a very broad range of possible dates: from the late 8th century B.C.E., attributing it those siege preparations by Hezekiah, to the 1st century B.C.E., in Hasmonean and Herodian times.

Clearly a more precise approach was needed. A team of radiocarbon experts led by Prof. Elisabetta Boaretto and Dr. Johanna Regev of the Weizmann Institute's Dangoor Research Accelerator Mass Spectrometry Laboratory were called in to study the find.

The researchers collected four organic samples from the mortar that held the brick wall together: a twig and three microscopic bits of straw. The straw is particularly important because, being a very perishable material, it would have had to be collected very shortly before it was mixed into the mortar, Boaretto explains. In other words, "the radiocarbon date is the date of the construction of the dam," she tells Haaretz.

All four samples returned similar dates, averaging out to a short window between 800-795 B.C.E., up to a century before the oldest previous estimates, which placed the dam's construction in Hezekiah's time.

The new dating puts the dam – and by extension the Siloam Pool – in the time of Jehoash of Judah, who reigned for 40 years in Jerusalem at the end of the 9th century B.C.E., or his successor Amaziah.

The dam may have been built as a response to climate change caused by the so-called Homeric Grand Solar Minimum, Regev, Boaretto and colleagues suggest. This period of low solar activity starting around 800 B.C.E. has been linked to cooler climate in Europe and lower overall precipitation in the Levant, accompanied by periodic torrential rainfalls and flash floods. The dam would have allowed to catch the rain from the occasional downpour and store the surplus water, the researchers conclude.

A white elephant?

While the new study makes it very likely that the dam was built around 800 B.C.E., the finding opens several new puzzling questions for researchers studying the history of Jerusalem, says Prof. Israel Finkelstein of Haifa University, a leading biblical archaeologist.

The Siloam dam and pool are located at the very southern end of the City of David and there is no evidence that Jerusalem had expanded to that area by 800 B.C.E. or to the nearby Western Hill (today's Armenian and Jewish quarters in the Old City), where evidence of significant settlement only appears a few decades later.

"I see no logic in investing in this project had it not been for the need to bring water to the new quarter," Finkelstein notes. Even more puzzling is the fact that the massive effort of creating the pool only makes sense if the site was behind a wall, protected from potential besiegers. Yet the walls surrounding the City of David have recently been dated, at the earliest, to the mid 8th century B.C.E., again a few decades after the apparent construction of the dam.

"So how do we square this circle?" Finkelstein asks. The question remains open, but it is possible that the city's expansion toward the Western Hill, what would later become the Old City of Jerusalem, was already starting by 800 B.C.E, albeit still undetected by archaeologists, and the pool and dam were meant to serve this new neighborhood, he says.

Be that as it may, there have been multiple archaeological discoveries in the City of David that have recently been dated to the time of Jehoash. These include the so-called "Spring Tower," a massive defensive structure that protected the Gihon, which was either built or refurbished (archaeologists differ heavily on this point) around 800 B.C.E.

There was also the recent bewildering discovery, in the northern part of the City of David, closer to the Temple Mount, of a giant moat whose purpose remains unclear, but which was also most probably dug in the time of Jehoash.

All this flurry of monumental activity points to a period of early expansion of Jerusalem at the turn of the 9th century B.C.E., most archaeologists agree. But opinions continue to differ over the origins of this sudden prosperity and how large the city was in these still early phases of the First Temple period, and the debate is likely to continue for many years to come.