From above, it seems as though a series of holes were pierced in the desert’s dry surface. But a hundred feet below the mysterious pits, a narrow tunnel carries water from a distant aquifer to farms and villages that wouldn’t exist without it.

These underground aqueducts, called qanats, are 3,000-year-old marvels of engineering, many of which are still in use throughout Iran. Beginning in the Iron Age, surveyors—having found an elevated source of water, usually at the head of a former river valley or even in a cave lake—would cut long, sloping tunnels from the water source to where it was needed.

The orderly holes still visible aboveground are air shafts, bored to release dust and provide oxygen to the workers who dug the qanats by hand, sometimes as far as forty miles. The tunnels eventually open at ground level to form vivid oases. (Watch: the secret history of saffron, the world's priciest spice.)

Constructing qanats was a painstaking task, made even more so by the need for great precision. The angle of the tunnel’s slope had to be steep enough to allow the water to flow freely without stagnating—but too steep and the water would flow with enough force to speed erosion and collapse the tunnel.

Although difficult work—even after completion, qanats require yearly maintenance—the irrigation tunnels allowed agriculture to bloom in the arid desert. The technology spread, through Silk Road trade and Muslim conquest, and qanats can be found as far as Morocco and Spain. (Read about the Persian legacy in modern Iran.)

For Komeil Soheili, an Iranian filmmaker who produced the video above, qanats are an integral part of the landscape of his native Khorasan Province.

“The diversity of landscapes and cultures [in Iran] is something that’s not well understood by the world,” Soheili says. “One of the oldest civilizations in the world came from this amazing creation, [the qanat.]” (See some of Iran's most wild and beautiful places.)

Gholamreza Nabipour, 102, is one of the last and almost certainly the oldest mirab, or caretaker of qanats. Recognized by the Iranian government as a national living treasure, Nabipour tries to share his craft with younger generations—including one of his sons, who uses a qanat to irrigate his pistachio farm—but fears for the future of this fragile tradition. (See Iran's centuries-old windmills in action.)

In the 1960s and 1970s, the subdivision of the large estates that relied on qanats caused an administrative tangle, and many qanats fell into disrepair without the traditional communal maintenance. And as modern agriculture takes root, Soheili explains, “people don't depend on qanats anymore, as it was before. It’s not possible to feed your family and earn money by working in qanats,” which have become less a way of life and more of a “hobby.”

In 2016, UNESCO listed the Persian qanats as a world heritage site.