Water · a Light

A Persian water tunnel older than Islam spread west with it

A qanat is a tunnel driven gently downhill from groundwater under a hillside out to the fields, so that water arrives by gravity and does not evaporate on the way. A line of vertical shafts marks its course across the desert, sunk to lift out the spoil and to let the diggers breathe. The technique is Iranian and pre-Islamic, at least two and a half thousand years old, and the one at Gonabad is still delivering water. Under Muslim rule it spread east and west and took local names: falaj in Oman, foggara in Algeria, khettara in Morocco, karez further east. Madrid drank from galleries of this kind into the nineteenth century. Around the year 1000 the mathematician al-Karaji wrote a book on finding hidden water and building these tunnels, with surveying instruments and rules for ventilation.

Qanats · Iran and westward, from c. 500 BCE