From the eleventh century onward, in connection with an expanding trade between regions and with countries abroad, the culture of the Swahili city-states asserted its status as one semi-periphery of the world-system, coevolving along with the system’s cores. Islam spread only along 1,500 kilometers of coastline – but not inland – a process clearly simultaneous, in time and space, with the development of towns and trade. As was the case in West Africa, Islam merged with African beliefs and practices (Insoll 2003: 172) (generally speaking, a semi-periphery exhibits politico-religious and economic organizational forms that derive from its dominant cores as well as from the peripheries from which it springs). Wright points out (1992) that Islam developed, not mainly in towns located near the Arabian heartland – in the north – but instead spread to the most significant trade centers, along the coast, and then on to secondary centers, along paths already traced by the networks. Hierarchized societies formed, based on both African and Arabo-Persian organizational principles.