Water is the thing you cannot take for granted in central Tunisia, and the Aghlabid emirs, who ruled from Kairouan in the ninth century, solved the problem with engineering. They built a series of reservoirs outside the city, fed by a channel that brought rainwater down from the hills to the west. The Great Basin is a huge round pool, about a hundred and twenty metres across, with thick buttressed walls and a small central pavilion, and it looks more like a stage than a tank. Next to it, a smaller settling basin allowed silt to drop out before the water flowed in.
Standing at the rim, you can imagine how important this was. Kairouan has hardly any natural water, and the basins supplied the city and its gardens when the desert wind blew. They fell out of use over the centuries, were restored in the nineteenth century, and now sit among dusty lots and modern houses, a bit sad but still impressive. The water is often low in summer, green and still, with birds on the surface and children fishing nearby, and the stone walls give the place a calm, almost sculptural look.
Getting here is easy, a short ride from the old city walls through streets of low houses. The tarmac is fine, but watch for potholes at the edges and for goats wandering across the road. A tour bus or two will usually be parked nearby, and small stalls sell postcards and carved souvenirs. Visit in the late afternoon when the low sun lights up the stone, and keep sun protection handy, as shade is scarce.
Kairouan, with its hundred and twenty thousand people, has everything for riders, from petrol stations on the main roads to hotels in converted houses. The next stage of the ride heads east toward El Jem, about sixty kilometres of flat road through olive groves, where the Roman amphitheatre rises dramatically out of the plain. Plan spring or autumn, and expect a hot, dry wind from the south in summer.