The Muslim conquest of the North African Mediterranean coastline was completed in the early 8th century: the territory divided into separate caliphates, with shifting borders and spheres of influence. To their south, Ghana, Mali, then Songhay would successively dominate the western Sahara, growing rich on the trade of gold, salt and slaves. On the West African coast, in the 15th century, Benin grew from a city-state to empire under Ewuare the Great. To the east, Ethiopia was ruled by the world’s oldest Christian dynasty, the Solomonids, with their capital at Axum. On Ethiopia’s northern borders, Nubia’s Christian kingdoms stemmed the Muslim southward advance, although the Adal dynasty of Somalia converted to Islam. In southern Africa, Great Zimbabwe was the stone capital of an empire built on the gold and ivory trade. This empire flourished until the early 1500s, when drought and a decline in trade caused its decline.