Place name origins only have little relation to the Roman names (e.g. Chester - 'Deva', Winchester - 'Venta Belgarum' etc.). Many English places derive part of their name from the river upon which they were built, but in the 16th century many English rivers were renamed with back-formations from towns on their banks. Cambridge, perhaps uniquely, illustrates both effects: originally "Grontabricc", a bridge on the Granta, the name became "Cantebruge" and then "Cambrugge", from which the river was renamed Cam. The vast majority of place names in Wales are Welsh by origin, containing elements such as Llan-, Aber-, Pen- etc. Along the south
England–Wales border Silures, traditionally the area between the rivers Usk, Wye and the Severn estuary. It was centred at different times on "Venta" (Caerwent), from which it derived its name, and "Isca Augusta" (Caerleon). Gwent generally allied with, and at various times was joined with, the smaller Welsh kingdom of Ergyng, centred in present-day southern Herefordshire west of the Wye (and deriving its name from the Roman town of "Ariconium"); and the larger kingdom of Glywysing in modern Glamorgan. The name Glywysing may indicate that it was founded by a British native of "Glevum" (Gloucester). The Battle of Mons Badonicus, circa 500,