A qanat is a gently sloping underground tunnel that taps an aquifer in higher ground, typically at the foot of mountains, and carries the water by gravity to fields and settlements on the plain, emerging at the surface without pumping. A line of vertical shafts along its course gave access for excavation and maintenance and appears as a string of spoil rings on the desert surface. The technique is generally traced to Iron Age Persia from around 800 BCE and could run for many kilometres while limiting evaporation losses. Construction and upkeep demanded specialised, dangerous labour and communal water-rights arrangements.
The qanat made permanent towns and irrigated agriculture possible across arid lands where surface water failed, supporting cities on the Iranian plateau and beyond. The technology diffused widely, from Iran across North Africa to Spain and, via Spanish colonisation, to the Americas, underpinning settlement patterns in dry regions for millennia.