Colonia
A colonia was a Roman city of the highest rank.

A colonia was the highest rank of Roman city. Normally all citizens of a colonia were also Roman citizens. Throughout the Empire period former legionnary bases were often converted to colonia by granting land to retired legionnaries. The thinking was that these legionnaries would raise families and provide future recruits to the legions, which were only open to Roman citizens.

The first colonia established in Britain was at Camulodunum (Colchester), around 49 AD. Camulodunum was followed by Lindum (Lincoln), and Glevum (Gloucester) at the end of the first century.

Each colonia was governed by an ordo (council), under the control of four quattuoviri (annually appointed magistrates).

The levels of Roman cities - in descending order - are as follows: Colonia Municipium Civitas capitals

Related:
Municipium
Civitas