The island of Britain was a mish-mash of Celtic tribal kingdoms in the south (England) and the "barbarian" tribes in the north (Scotland) until Rome invaded under the Emperor Claudius (CE 69). Rome consolidated its power in the lower half of the island, though the hand of Rome never extended beyond Hadrian's Wall (begun in CE 122) for long (there was a brief expansion to the Antonine Wall between CE 140 and 163).

The Roman policy of establishing client kingdoms, where the native ruler was allowed to remain in power if he paid tribute to the Empire and did not rebel, cushioned the transition in the south (Scullard 50). The premise of the laiti (Lang 52) was for Rome to establish for each tribe a civitas-- a town centered on the old tribal lands, where the members of the tribe could live and slowly become assimilated to Roman ways, while remaining "of the tribe" (Scullard 49). It is when Rome deviated from this policy of subtle transition that the Empire encountered rebellion in Britain.

A specific example of this: after the chieftain of the Iceni tribe died, Rome by-passed the traditional rights of the heirs-- in this case, the chief's wife, Boudicea-- and attempted to simply absorb the Iceni lands (there was also the rape of her daughter involved). An incensed Boudicea rallied her husband's men, and several bloody battles ensued, with the Iceni as the victors. Rome eventually suppressed the revolt, and put the Iceni under military rule for some time before finally establishing the Iceni civitas of Venta Icenorem (Caistor-by-Norwich) (Scullard 50).

Before the reorganization of the Empire by Diocletian, Roman Britain was divided into two main parts. The southeastern part of the island was Britannia Inferior, composed of civilian settlements populated by a comfortable blend of Roman immigrants and assimilated Celts. A line drawn by Fosse's Way (the road extending from Isca (Exeter) to Lindum (Lincoln)) separated this "civilian" zone from the northwest, which was under military occupation. This military zone, Britannia Superior, extended all the way to Hadrian's Wall. Rome's control never went beyond Hadrian's Wall for more than a few years, and Rome never brought Ireland under its control, either.

Under pre-Diocletian Roman rule, five towns were given the rank of municipia, or coloniae, which granted the inhabitants Roman citizenship and rights. Among these were Eboracum (York) and Lindum (Lincoln); London was not granted this status, though the River Thames had already made it an important city.

Diocletian divided the empire into twelve dioceses, each governed by a vicarius. When Britain was made a diocese, London came into its own, as the local vicarius was based there. He was the highest political authority in Britain, reporting only to the praetorian prefect of Gaul, Spain and Britain. The diocese of Britain itself was divided into four provinces, each governed by a praesides. Britannia Prima (essentially Wales) was centered on the capitol of Corinium (Cirencester). Britannia Secunda was the north country, centered on the Eboracum (York). Maxima Caesarientsis in the south (centered on London) went through a few name changes. It was renamed Caesara for a time, until finally it was called Augusta. The fourth province was Flavia Caesariensis was eastern, and centered on Lindum (Lincoln). In CE 369, a fifth province was added north of Britannia Secunda, with a capital at Carlisle (Scullard 171).

Trouble back in Italy led to the abandonment and isolation of Britain by Rome throughout the late 4th and early 5th centuries. Some Roman troops were withdrawn, others simply drifted away, marrying with the local populace or leaving Britain altogether. The areas that had been the first purchase of Roman civilization on the island were the first to fall before the Saxons.