These cisterns, built by the Aghlabids in the 9th century, are more impressive because of their engineering sophistication than as sights in themselves. Water was delivered by aqueduct from the hills 36km west of Kairouan into a smaller settling basin and then into an enormous main holding basin, which was 5m deep and 128m in diameter. In the centre of the main pool was a pavilion where the rulers could come to relax on summer evenings.
Though entry to the basins is officially included in the Kairouan multi-site day ticket, in reality they are open 24 hours and free to enter. A good view of the site can be had from the roof terrace of the nearby tourist office.