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