How it began
Kairouan, founded in 670 in the middle of an arid steppe in present-day Tunisia, had no river nearby, so supplying water was a constant concern. In the 9th century, when the city was the center of the Aghlabid Emirate, the ruler Abu Ibrahim Ahmad (reigned 856 to 863) commissioned two large reservoirs north of the old city. They were built between 860 and 862 under the supervision of Khalaf al-Fata, a freed slave in his service. They belonged to a group of about 15 reservoirs, of which two survive.
Before it existed
According to the 11th-century geographer al-Bakri, the Umayyad caliph Hisham (reigned 724 to 743) had ordered 15 reservoirs outside Kairouan, which have not survived. Many residents relied on private wells and cisterns in their houses. The Aghlabid reservoirs supplemented these in drought and supplied livestock and caravans.
How it works
Each reservoir is a chain of parts. Water from the countryside first entered a small basin, in the larger reservoir a 17-sided polygon 37.4 meters across holding 4,000 cubic meters, where sediment settled out. When the level rose, water spilled through an outlet into the large basin, a 48-sided polygon 128 meters across and 4.8 meters deep with a capacity of over 57,000 cubic meters. From there it passed into two vaulted cisterns with openings in the roof for drawing water. The walls are rubble stone with a waterproof coating and rounded buttresses.
How it spread
Water reached the basins from the Oued Merguellil and its tributaries through small dams, weirs and canals, and by an aqueduct from springs in the Shreshira hills 36 kilometers to the west, which reused some Roman works. Another Aghlabid reservoir was built for the new capital at Raqqada, founded in 876. In 961 the Fatimid caliph al-Mu'izz refurbished the aqueduct and added a second channel.
Where it stands today
Two reservoirs survive a short distance north of the medina of Kairouan. A masonry pillar in the middle of the largest basin may be the base of a domed pavilion described by al-Bakri. A 70 meter elevated section of the aqueduct is preserved near the town of Haffouz.
