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Jerusalem yields 'natural' waterworks.

For more than 100 years, archaeologists and historians have puzzled over the haphazard routes, slopes and dimensions of two underground water supply systems discovered beneath the remains of ancient Jerusalem. Although most researchers regard the subterranean waterworks as the products of early, error-prone engineers and construction workers, a new analysis indicates that residents of the holy city skillfully altered a natural network of underground channels and tunnels to ensure a dependable water supply.

Knowledge of the natural passages snaking beneath Jerusalem's defensive walls may have helped the army of David to mount a successful surprise attack -- alluded to in the Old Testament -- on the city's inhabitants about 3,000 years ago, asserts Israeli geologist Dan Gill in the Dec. 6 SCIENCE.

The dual water networks, built several centuries after David's victory, ferried water into the city from the nearby Gihon Spring, says Gill, of the Geological Survey of Israel in Jerusalem. One system consists of a horizontal tunnel that fed water into a vertical shaft serving as a well, from which water was hauled into an upper tunnel leading farther into Jerusalem. Water also ran through an underground canal to an aboveground reservoir within the city walls.

Geologic clues indicate the underground waterworks resulted from a careful refashioning of natural channels and shafts that had formed in the limestone beneath the city over millions of years, Gill says. For instance, the vertical shaft displays an irregular shape and calcium crust typical of a natural sinkhole, he notes. Ancient residents of Jerusalem probably tracked the limestone fissure leading to the sinkhole and fashioned it into the roughly level lower canal, transforming the shaft into a well. During this process, limestone hewers apparently discovered a branch of the fissure that they eventually hollowed out into the underground canal, Gill contends.

The natural formation of underground channels in limestone also produced the GihonSpring, he says. "Gihon" translates as "gusher," referring to intermittent pulses of water typically triggered by subterranean passages that act as a periodic siphon, according to Gill.

Because workers followed existing passageways, the waterworks sometimes veer in random directions, contain unnecessarily high ceilings and display other apparent mistakes, he maintains. Interconnected channels and sinkholes branched off from the water supply system and reached the surface, providing ventilation for tunnelers.

Some biblical scholars have interpreted sections of the Old Testament as describing David's use of a hidden passage to capture Jerusalem. The new study supports these claims by establishing that the ancient city contained two underground openings that emerged outside its walls, Gill points out.
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Author:Bower, Bruce
Publication:Science News
Date:Dec 7, 1991
Words:423
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