Breguion is the name given to Mount Agned, according to one tenth-century manuscript. The site of one of Arthur’s battles against the Saxons, according to Nennius.
In some manuscripts, the name of the mountain is Agned. William Camden thought that Mount Bregion (Cath-Bregion) was located at Cadbury.
Nennius may have been connecting to Arthur a victory actually achieved by Urien (Uriens) at Brewyn.
Historia Brittonum | Probably Nennius, early 9th century
Britannia | William Camden, 1586