This chapter explores the development of mosques and Islam on the coast, situating the emergence of the first coral-built mosques by 1000 ce and their constituent materials. It examines the nature of co-constitutive entanglements, as possible demonstrations of devotion or a quieter means of building in local powerful forces in the context of a foreign religious locale. In general, by 1000 ce, the Swahili world expanded outward, as they become more maritime oriented, and actively engaged in the larger Indian Ocean world. Researchers of the Swahili have understood the way mosques can serve as a locus of human gathering, as Muslim adherents travel to the mosque multiple times a day or, at the very least, every Friday. The chapter explores what is known about the evolution of Islam in Swahili towns, charting developments from 780 to 1500 ce and the emergence of the first coral-built mosques at 1000 ce.