Iran is a desert but with mountains, a condition that allowed the Iranian civilization to invent the qanat, a passive water mining device that led to the invention of the garden and by extension the city. The qanat directs water from the underground aquifers deposited at the foothill of a mountain by infiltration of melted snow. That is why ninety percent of all cities in Iran are located precisely there, at the foothill. Imitating the movements of water on soil, an underground network is dug. Relying purely on gravity, the natural slope of the ground is used to distribute water to lower sources in the cities, gardens, and fields. In fact in Farsi the word abadi translates as city, designating literally the place to bring water. The qanat generated an entire civilization: the garden, the house, and then the city. Vitruvius references the qanat with technical details in 18 BC in what is known historically as the first architectural treaty, De Architectura. There are over three hundred thousand kilometers of qanat in Iran, a network forming the equivalent of the distance between the earth and the moon. In Tehran, there are over 600 abandoned qanats.