Biblical Tunnel Authenticated by Radio-Dating

September 10, 2003

Photo: The Siloam pool is still replenished by the tunnel today (Image: Israel Nature and Parks Authority)

Biblical accounts of the construction of an ancient underground tunnel below Jerusalem have been verified by dating the material lining its walls.

The books of Kings and Chronicles report that the Siloam tunnel was built by King Hezekiah, ruler of Judea 2700 years ago. Its aim was to provide a secret source of drinking water should the city face a siege by Assyrian assailants. Even today, the tunnel delivers water from the Gihon Spring to the Siloam Pool, 500 metres away.

Some scholars have questioned the biblical account, suggesting that the tunnel, which is up to 30 metres below ground, was built 500 or so years later. But a team led by Amos Frumkin of the Hebrew University of Jerusalem has now settled the argument by radio-dating the tunnel's lining.

Frumkin says the tunnel, just 60 centimetres wide and between one and five metres in height, is the first biblical structure dating from the Iron Age to be authenticated.

Many similar sites are impossible to visit and take samples from, he told New Scientist, either because they are so deteriorated or for religious and political reasons.

Uranium and thorium

Frumkin and his colleagues found plant material in the plaster lining the tunnel, and stalactites that began to grow from the ceiling shortly after its completion.

Plant material and stalactites were used to date the tunnel (Image: Israel Nature and Parks Authority)

They then used radio-isotope dating to establish how old they were. This exploits the fact that the half-life for the decay of a radioactive element is fixed. Measuring the proportions of the radioactive element and its decay products therefore gives an estimate of age.

For the plants, carbon dating was used, measuring the carbon-13 isotope and is decay product carbon-12. For the stalactites, isotopes of the elements uranium and thorium were measured.

"They're two complementary methods," says Frumkin. Taken together they indicate that the tunnel originated about 700 BC, as stated in the Bible. "It verifies the biblical account, and that King Hezekiah was responsible."

Frumkin says that an inscription had been left on the tunnel wall, commemorating the meeting of the two teams of diggers approaching one another from opposite directions. "But it doesn't say who dug the tunnel, so it remained a mystery," he says.

Equally mystifying, adds Frumkin, is how the teams found each other given their meandering paths. But somehow they managed, and the inscription describes how they could hear each other when they were about 1.5 metres apart.

Journal reference: Nature (vol 425, p 169)

Andy Coghlan

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