Spanning c. 1050–1500 CE, a burgeoning Swahili community called Chwaka built a sequence of four mortared coral mosques in their town of wattle-and-daub houses on Pemba Island, Tanzania. The mosques’ placement, construction, and use played an active role in creating and strengthening an Islamic community and help us define changes in social practice within the town and the larger polity in which it existed. It is argued that the construction of each mosque was an act of assembling, drawing people, other-than-human things and affective social practices together in ways that help tell an urban story. This research provides insights into the residents’ socioeconomic and cultural priorities and the town’s changing relationship with villagers from the surrounding region, contributing to understandings of Swahili urbanism and urban practice.