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
Venta Silurum to the emerging Kingdom of Gwent (called initially "Kingdom of Guenta"), and the town itself became known as "Caer-went" or "the castra/fort of Venta/Gwent". Tradition holds that Caradog Freichfras of Gwent moved his court from Caerwent to Portskewett around the 6th century. The town lacked substantial defences until the mid 4th century when stone town walls were built. A small garrison may have been based in the town during this period. Large sections of the defensive walls are still in place, rising up to 5 metres in height in places. The walls have been described as "easily the most impressive