The qanat (کاریز) is a system of underground channels that transports water from an aquifer in mountainous areas to arid farmland, relying exclusively on the topographic gradient, with no pumping mechanism whatsoever. It is built by excavating a horizontal gallery that intercepts the water table, flanked by equidistant ventilation and access shafts used for sediment removal and maintenance. The oldest archaeologically dated Iranian qanats correspond to the 8th century BC in the Gonabad region (Khorasan); Assyrian inscriptions from the same period describe the capture of specialized Persian engineers, confirming an origin in the Medo-Persian world prior to Cyrus the Great. The system was adopted as state infrastructure by the Achaemenid Empire. Iran currently operates more than 37,000 qanats, some with more than 2,700 years of documented continuous operation. Persian qanats were inscribed on the UNESCO World Heritage List in 2016. The system spread with the Islamic conquests throughout the Arab world, Al-Andalus, and North Africa, where it left a lasting terminological and topographical imprint.