The region now known as Gloucestershire was originally inhabited by Brythonic peoples (ancestors of the Welsh and other Romano-British 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, previously 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. Military significance Gloucestershire formed part of Harold's earldom at the time of the Norman Conquest of England, but it offered slight resistance to the Conqueror. During The Anarchy, Empress Matilda was supported by her half brother, Robert of Gloucester, who had rebuilt Bristol Castle. The castles at Gloucester and Cirencester were garrisoned on her behalf. Beverston Castle was also a site of the conflict. In the barons' war of the reign of Henry III, Gloucester was garrisoned for Simon de Montfort, but was captured by Prince Edward in 1265, in which year de Montfort