Today, we talk about qanats. (Betcha don't know what a qanat is!) The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Jakob Bronowski included an eerie scene in his Ascent of Man series on TV. It's in his program on the origins of agriculture. It's a desert scene. An Arab woman passes through an entry in the sand. She walks down, down, into the earth. Far under the surface she draws water from a long subterranean canal hewn through rock. The canal runs for miles. An aerial photo shows access shafts, a hundred feet apart, running down to the canal far below.

Geographer Dale Lightfoot writes about those watercourses. They're called qanats and they are remarkable constructions. The oldest ones we know about were built in Persia some 2700 years ago. Qanats were built throughout the fertile crescent. Then, when Islam spread Arab culture to the west in the 8th century, qanat building followed all the way to Spain, and beyond.

Qanats run under sloping ground. At the high end, a vertical mother shaft is dug down into an aquifer. A horizontal tunnel carries water away from the aquifer to the spot, maybe one mile away, maybe 40, where the tunnel meets the surface of the land. There, water emerges to irrigate low-lying farm lands. The access shafts let people lower themselves to the main tunnel in baskets. There they can draw water, or they can clear trash from the tunnel.

With all our pumps and power supplies, we have trouble understanding qanats. If we want ground water, we drill into an aquifer, pump the water out, and distribute it in pipes. But that wasn't possible until a few hundred years ago. While qanats take a vast investment of labor, once they're built they last until either the aquifer dries up or civilization forgets they're there.

Local people cut these vast tunnels through limestone and dense alluvial soil. The Romans weren't very inventive; but they fancied great engineering works. So they did a lot of qanat building after they conquered Syria. The irony of that is, modern Syrians speak of Roman qanats when they aren't a Roman idea at all. In any case, some 239 qanats are scattered through Syria alone.

The depth of those old water courses was anywhere from 30 to as much as 300 feet at the mother shaft, depending on the rainfall and the geology of the aquifer. The underground canals were typically five feet in height. With all that digging, these projects take their place right along with the ancient wonders of the world.

Water is a primal theme in the dry Middle East. Fountains recur in Arab architecture and Arab literature. The action of the Old Testament also moves from one spring or well to the next, and the sacramental importance of water is apparent from the beginning. Once we learn about these astonishing tunnels, we realize we've found much more than remarkable works of engineering. We have, in fact, found the very soul of an ancient people.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Lightfoot, D. R., QANATS in the Levant: Hydraulic Technology at the Periphery of Early Empires. Technology and Culture, Vol. 38, No. 2, April 1997, pp. 451.

Bronowski, J., The Ascent of Man. Boston: Little, Brown and Company, 1973, Chapter 2, The Harvest of the Seasons. (This is also available on videotape and film.)

I am grateful to Dale Lightfoot, Oklahoma State University Department of Geography, for his counsel on this episode.