I now believe I was onto something, and that work I've done in recent months supports this idea. Some additional posts relating to this will be coming soon. For now, I will content myself with bringing this theory back to life for examination by others.]
The Isle of Islay, where Arthur slew the Irish king Mongan
The famous Arthurian battle list of the HISTORIA BRITTONUM is found immediately after mention of Octha's (Octha = Aesc) ascension to the throne of Kent in 488. Arthur is said to have fought against “them”, and the contextual implication – often ignored – is that the “them” is question are the Kentish Saxons.
We know of the following 6th-7th century Arthurs, discounting for a moment Nennius's Arthur dux bellorum:
Arthur son of Aedan (or Conaing) of Dalriada
Arthur grandfather of Feradach (mentioned in connection with St. Adomnan,
and thus probably also of Scotland)
Arthur son of Petr (the Irish Petuir or Retheoir)
Arthur son of Bicoir the Briton
What I asked myself, in looking at these various Arthurs, is why one of them would have been placed by the HISTORIA BRITTONUM narrative right after mention of Aesc of Kent and in the southern England of the early Wessex dynasty. No answer revealed itself, until I looked at year entry 625 of the Irish Tigernach Annals:
... Baptismum Etuin maic Elle, qui primus credidit in reghionibus
Saxonum... Mongan mac Fiachna Lurgan, ab Artuir filio Bicoir Britone
lapide percussus interit. Unde Bed Boirche dixit
IS uarin gaeth dar Ile,
do fuil oca i Cind Tire,
do-genat gnim amnus de,
mairbfit Mongan mac Fiachnae.
The translation of the regular entry tells how Arthur son of Bicoir, a Briton, killed Mongan, King of Ulster, with a stone. Immediately prior to the entry on Artuir son of Bicoir we are told of the baptism of Edwin son of Aelle of Northumbria, an event mentioned under the year 627 in the Anglo-Saxon Chronicle.
The poem stanza is translated as follows:
Cold is the wind over Islay;
there are warriors in Kintyre,
they will commit a cruel deed therefor,
they will kill Mongan, son of Fiachna.
Now, the implication is, of course, that Arthur is from or at least "in" Kintyre, which was part of Dalriada, the later Argyle. However, compare the Old Irish Cind Tire/Kintyre with the following entry from the Anglo-Saxon Chronicle, which tells of the 457 Crecganford battle featuring Hengist and his son, Aesc. And bear in mind that it is this Aesc – or Octha, as Nennius calls him - who is mentioned as succeeding to the kingship of Kent just prior to the listing of the Arthurian battles.
Her Hengest 7 Aesc fuhton with Brettas in thaere stowe the is gecueden
Creganford 7 thaer ofslogon .iiiim. wera, 7 tha Brettas the forleton
What I am proposing is that the Cind Tire of the Artuir passage in Tigernach was interpreted as Cent/"Kent" + Welsh tir (cf. L. terre, "land, earth, country") and equated with the Centlond of the ASC entry for the year 457. It is also possible that the Elle/Aelle mentioned in Tigernach 625 may have been identified with the much earlier Aelle of Sussex, who is mentioned in the Chronicle just prior to Cerdic. With Arthur now in Kent, the author of the HISTORIA BRITTONUM appropriated Cerdic of Wessex's battles to further glorify this imaginatively created Dark Age British hero.
The famous Arthur of legend would appear to have originally been Arthur son of Bicoir - if we could get by the grave problem of incorrect chronology. And if we could get past the fact that Arthur derived from Artorius can only be associated with the York area, and all the battles of Arthur in the Historia Brittonum show a chieftain in northern England and Southern Scotland.