This article examines evidence for community among immigrants in ancient Transtiberim (modern Trastevere), a section of Rome that was both socially and spatially distinctive for much of the city's history. The only part of Rome located on the west bank of the Tiber River, Transtiberim was the heart of Rome's Jewish and Syrian communities. These immigrants and their descendants maintained certain traditions, languages and customs from home; participated in civic institutions that helped foster community at the local level; and laboured in institutions that were vital to the capital's urban economy. Though marginal in some ways, Transtiberim was also a neighbourhood where immigrants and their descendants found community and made vital contributions to the life of the imperial city.