Tichit's architecture exists nowhere else in Mauritania. The land around it yields six distinct colors of stone, and the builders here did something the rest of the country did not: they shaped the stones, then arranged the colors into patterns set into the walls. Houses, courtyards, and boundary walls become quiet geometry, dark and pale stone laid up into designs against the sand-colored desert. The great mosque is built entirely from blue-grey stacked stone and ranks among the most celebrated in the country. Even the cemetery carries the local signature, marked out in the unusual green stone found in these hills. The whole town is, in effect, a mosaic assembled from the ground it stands on.

Tichit is, above all, a salt town. For almost a thousand years it has been a trading center for salt, and it was salt that drew the camel caravans across the desert to its gates. The town once held a Koranic school, and though that scholarly life has faded, it left behind a legacy of ornate mosques that punctuate the bare landscape like landmarks. Set on the high plains at the foot of the Tagant escarpment, Tichit sits along the long cliff line that fringes the Aoukar basin, a string of desert towns strung out where the highland meets the vanished lake, all of them once links in the same trans-Saharan chain of trade.

The medieval town is a UNESCO World Heritage Site, inscribed in 1996 as one of the four Ancient Ksour of Mauritania alongside Ouadane, Chinguetti, and Oualata, fortified caravan towns that served the desert trade routes. But Tichit's roots run far deeper than the medieval. Nearby lie the remains of communities dating to around 2000 BC, part of the Dhar Tichitt settlements that gave their name to the whole early culture of the region. These are the oldest surviving archaeological settlements in West Africa, and the oldest stone-built settlements anywhere south of the Sahara. To stand here is to stand at one of the deepest foundations of West African urban life.

Tichit is not a ruin. Fewer than fifteen hundred people still live here, speaking Hassaniya, working the date palms, and keeping the old stone town alive at the desert's edge. The date harvest is the year's great event: the picked dates are heaped into mounds, covered with palm fronds and then sand to keep them, a method as old as the town itself. In the market a patient visitor can still find very old beads and stone grinding tools, the small worn objects of a long human presence. And driving in, before any of it, you meet the dunes, endless white sand receding to the horizon, the desert that has been slowly closing in on Tichit for centuries and has not taken it yet.