Civitas
The basic administrative district of Roman Britain was the civitas.

Roman Britain was divided into civitas, or towns loosely based on pre-existing Celtic tribal territories. The civitates (Latin plural form of civitas) were independent administrative centres, governed by the Celts themselves, though under the supervision of Roman provincial administration based in London. These civitates generally used the same structure of government as municipia, that is, an elected council and magistrates.

The Romans invited the old Celtic aristocracy to administer the civitates. By involving their conquered foes in the government, they made allies of possible enemies, and at the same time avoided the expense of administering their new province on their own. Thus, in a gradual way, did the Celtic aristocracy become Romanised.