The belief that the historical King Arthur belongs to the south-west of Britain is an ancient association. A visit to Cornwall in 1113 by some canons from Laon found that the Cornish believed King Arthur will come to liberate them, and noted that the Bretons have the same legend.
Another south-west tie to Arthur is that all the early sources – the 12th-century Welsh poets, the Trioedd Ynys Prydein (the Welsh Triads), and Culhwch ac Olwen (which has been variously dated from the mid 10th-century to the late 11th-century) – agree that Arthur’s court was called Celliwig (‘the forest grove’) and was in Cornwall.
Other evidence for an association of Arthur with south-western Britain includes the mid-late 9th-century poem Gereint fil[ius] Erbin; the Vita Prima Sancti Carantoci (c.1100), which mentions a dragon-slaying episode in Somerset; the story of Gwenhwyfar’s abduction and imprisonment at Glastonbury in the Vita Gildae of Caradoc of Llancarfan (1120s or 1130s); and Geoffrey of Monmouth’s story of Arthur’s conception at Tintagel, Cornwall
The discovery of Arthur’s grave in the 1190s by the monks at Glastonbury Abbey is not really accepted by anyone today as real. Cadbury Castle, Somerset, which was an important Iron-Age hill-fort was reoccupied and heavily refortified in the late 5th- or 6th-century by a powerful warlord and there was alocal folk lore that this site was Arthur’s Camelot.
Historia Brittonum is the only real source of information on any historical Arthur and the most that can be inferred from this source is that Arthur was a late 5th-/early 6th-century war-leader, famed for leading the fight against the Saxon invaders and winning a victory at the Battle of Badon. And this victory is his main reason for being recorded in Historia Brittonum, so it would seem logical that Badon lay within Arthur's shpere of operation, and that if we knew where Badon was, we would have a handle on where Arther lived.
So, where was Badon? Badon has not actually been accurately identified. Most researchers agree that this battle was fought somewhere in southern Britain. Archeology shows too that most Sxon settlements from 5th and 6th century were in the south and east of Britain, making this the most likely region for British war-leader fighting the invaders to be operating in.