One of the Berber groups arriving in Mauritania in the eighth century was the Lemtuna. By the ninth century, the Lemtuna had attained political dominance in the Adrar and Hodh regions. Together with two other important Berber groups, the Messufa and the Djodala, they set up the Sanhadja Confederation. From their capital, Aoudaghast, the Lemtuna controlled this loose confederation and the western routes of the Saharan caravan trade that had begun to flourish after the introduction of the camel. At its height, from the eighth to the end of the tenth century, the Sanhadja Confederation was a decentralized polity based on two distinct groups: the nomadic and very independent Berber groups, who maintained their traditional religions, and the Muslim, urban Berber merchants, who conducted the caravan trade.

Although dominated by the Sanhadja merchants, the caravan trade had its northern terminus in the Maghribi commercial city of Sijilmasa and its southern terminus in Koumbi Saleh, capital of the Ghana Empire. Later, the southern trade route ended in Timbuktu, capital of the Mali Empire. Gold, ivory, and slaves were carried north in return for salt (ancient salt mines near Kediet Ijill in northern Mauritania are still being worked), copper, cloth, and other luxury goods.

Important towns developed along the trade routes. The easiest, though not the shortest, routes between Ghana and Sijilmasa were from Koumbi Saleh through Aoudaghast, Oualâta, Tîchît, and Ouadane. These towns along the route grew to be important commercial as well as political centers. The eleventhcentury Arab chronicler, Al Bakri, describes Aoudaghast, with its population of 5,000 to 6,000, as a big town with a large mosque and several smaller ones, surrounded by large cultivated areas under irrigation. Oualâta was a major relay point on the gold and salt trade route, as well as a chief assembly point for pilgrims traveling to Mecca. Koumbi Saleh was a large cosmopolitan city comprising two distinct sections: the Muslim quarter, with its Arab-influenced architecture, and the black quarter of traditional thatch and mud architecture, where the non-Muslim king of Ghana resided. Another important Mauritanian trade city of the Sanhadja Confederation was Chinguetti, later an important religious center. Although Koumbi Saleh did not outlive the fall of the Ghana Empire, Aoudaghast and particularly Oualâta maintained their importance well into the sixteenth century, when trade began shifting to the European-controlled coasts.