Ouadane lived and died by the trans-Saharan trade. Caravans hauled slabs of salt from the mines at Idjil, roughly 240 kilometers to the northwest, and the town grew rich as an entrepot - a place where goods were gathered, taxed, and traded onward. Its deeper fortune may have come from gold. In the 11th century the Arab geographer al-Bakri described a route carrying gold north during the era of the Ghana Empire, and historians have long argued over whether that road ran through Ouadane or skirted the escarpment to the east. Either way, the town sat astride a commerce that connected the goldfields of West Africa to the markets of the Mediterranean, ninety-three kilometers northeast of its sister city Chinguetti.

Outsiders noticed Ouadane's wealth. The first written record of the town comes from 15th-century Portuguese accounts; the chronicler Gomes Eanes de Zurara called it the most important town of the Adrar and the only walled one. In 1487 the Portuguese went further, building a trading post here in a bid to tap the desert flow of gold, salt, and enslaved people - though the venture seems to have been short-lived. In the 16th century the Moroccans pressed their own claim, launching military expeditions to occupy Ouadane in 1543-44 and again in 1584. Their wider campaign to seize the Saharan trade culminated in 1591 at the Battle of Tondibi, where Moroccan victory shattered the Songhai Empire to the south. Through it all, estimates put Ouadane's population in the low thousands - a small place that great powers nonetheless considered worth fighting for.

Climb through the old town and its history is legible in stone. The upper section, Tegherbeyat, is almost certainly the oldest; it once held a mosque, but nothing of it survives. The lower town, which grew as the settlement expanded, contains a mosque probably built in the 15th century. Some of its horseshoe arches still stand, and patches of clay plaster cling to the walls, suggesting the building was not abandoned until sometime in the 19th century. The structure was modest but carefully made: a terrace once supported by five rows of arches, an external mihrab at the eastern end, a courtyard for prayer in the brutal heat. To walk among these walls is to read the autobiography of a town in the language of stone and shadow.

Ouadane holds one last distinction: it is the closest town to the Richat Structure, the vast bullseye of concentric rings - some forty kilometers across - that astronauts use as a landmark and that early orbital crews mistook for an impact crater. It is now understood to be a deeply eroded geological dome, the Sahara's most famous feature seen from space. There is a fitting symmetry in this. For a thousand years Ouadane was a fixed point that travelers steered toward across a trackless desert; now it sits beside the one mark on this landscape visible from orbit. The caravans are long gone, the salt road silent, but the town still keeps its watch at the edge of the great Eye of the Sahara.