Civitas means citizenship, either of a Roman or of any peregrine (ie non-Roman) community. It was very commonly used to describe the peregrine communities themselves, so for example in Britain, each major tribal group such as the Atrebates was a civitas, with a major town as its administrative centre usually referred to today as a civitas capital, in this case Silchester (Calleva atrebatum). The legal status of towns sometimes changed during the course of the Roman period; for example Carlisle appears to have acquired the status of the Civitas capital of the Carvetii in the 3rd century.

Civitas capitals, though important in terms of administration, were not necessarily large - Caistor-St.-Edmund in Norfolk (Venta Icenorum) was only 14ha within its walls.