Along the East African seaboard, from Mogadishu to Kilwa and Sofala, a chain of Swahili city-states grew on Indian Ocean trade, exporting gold, ivory and timber for Asian ceramics, cloth and beads. Their merchants built in coral rag and lime mortar, quarrying living reef coral to raise multi-storey stone houses, congregational mosques and palaces such as the Husuni Kubwa at Kilwa. The towns combined a cosmopolitan Islamic urban culture with a distinctly African Swahili language and society. Kilwa controlled the gold trade from Great Zimbabwe's hinterland at its height.
The Swahili coast produced a durable indigenous tradition of coral-stone urbanism and made East Africa a full participant in the medieval Indian Ocean trading world, not a periphery of it.