The region now known as Gloucestershire was originally inhabited
by Brythonic peoples
(ancestors of the Welsh and
other British Celtic peoples) in the Iron Age and Roman periods. After the Romans left Britain in the early 5th century, the Brythons
re-established control but the territorial divisions for the post-Roman period are uncertain. The city of
Caerloyw (Gloucester today,
still known as Caerloyw in modern Welsh) was one centre and Cirencester may have continued as a tribal centre as well. The only reliably attested kingdom is
the minor south-east Wales kingdom of Ergyng, which may have included a portion of the area (roughly the Forest of Dean). In the final quarter of the 6th
century the Saxons of Wessex
began to establish control over the area.
The English conquest of the Severn valley began in 577 with the victory of Ceawlin at Deorham, followed by the capture of
Cirencester, Gloucester and Bath. The Hwiccas who occupied the district were a West
Saxon tribe, but their territory had become a dependency of Mercia in the 7th century, and was not brought
under West Saxon dominion until the 9th century. No important settlements were made by the
Danes in the district.
Gloucestershire probably originated
as a shire in the 10th
century, and is mentioned by name in the Anglo-Saxon
Chronicle in 1016. Towards the close of the 11th century the
boundaries were readjusted to include Winchcombeshire, hitherto a county by itself, and at the same time the forest district between the
Wye and the Severn was added to
Gloucestershire. The divisions of the county for a long time remained very unsettled, and the thirty-nine
hundreds mentioned in the Domesday Survey and the thirty-one hundreds of the Hundred Rolls of 1274 differ very widely in name
and extent both from each other and from the twenty-eight hundreds of the present day.