A quick outline of how I got to where I now find myself...

Dinas Emrys

 ...in terms of being able to identify a historical Arthur:

1) I was struck by the fact that the 6th-7th century Arthurs, subsequent to the more famous one, all belonged to Irish-descended dynasties in Britain.  No one had been able to adequately explain why this was so.

2) The floruits for Arthur and Cerdic of Wessex perfectly correspond.  These are nicely determined by a comparison of the relevant passages in the Historia Brittonum and the Anglo-Saxon Chronicle.  This led me to ask a couple of obvious questions: was Arthur being put forward as a British counter to Cerdic?  As Arthur Cerdic's opponent?  Or, since Cerdic was certainly Celtic, could Cerdic be Arthur?

3) I had already surmised that Cerdic was Ceredig son of Cunedda.  I also knew with a fair degree of certainty that Cunedda was the Irishman Cuinedha Mac Cuilinn.  Cunedda had a grandson (actually son, as the intervening 'Gwron' is not a name, but merely a word meaning 'hero') named Cynyr, W. cognate to the Cunorix found with Maquicoline at Wroxeter.  Could -coline be the Gewissei Ceawlin?

4) I had spent a couple of years working on the Welsh material - the 'pre-Galfridian' sources - concerning Arthur. Of particular importance was his father, Uther.  Uther was related to the men of Caer Dathal in Arfon, Wales.  Caer Dathal was unidentified.  I successively identified it with Dinas Emrys in Beddgelert parish.  Gelert/Celert I proposed (and had the proposal accepted by Peter Schrijver and others) was for L. Celeritas.  This matched the meaning of the Irish name Dathal.  Therefore, the original name of Dinas Emrys was Caer Dathal.  This was the original home of Arthur's father - NOT Tintagel in Cornwall.  A linguistic comparison of Tintagel and Caer Dathal showed that the two names could easily have been confused for each other or intentionally substituted for each other.  

5) Uther is a problem as a name, precisely because it is merely an adjective.  It had long been suspected that 'terrible/horrible chief of warriors' was merely a title, not a name + epithet.  If so, I had to find Uther's real identity.

6) In the Historia Brittonum folktale on Ambrosius, the boy is given all of Gwynedd by Vortigern.  This is strictly nonhistorical.  The only one we know of who actually took all of Gwynedd in this period is Cunedda and his sons.  Uther and Ambrosius are linked in tradition with Dinas Emrys, and I had shown that Uther's Caer Dathal was Dinas Emrys.  Could Uther be Cunedda?

7) The answer to that question lay in the strange 'pen kawell' phrase in the elegy poem on Uther Pendragon.  Taken literally, it means 'Chief Basket' or, perhaps, 'Chief of the Basket.'  Not knowing AS, and on a whim, I looked up ceawl- in the Bosworth and Toller dictionary.   The name meant 'basket.'   While a very tenuous basis for identification, I tentatively decided to go with Uther = Cunedda/Ceawlin.

8) Ceredig son of Cunedda now needed additional exploration.  I found that in his kingdom of Ceredigion there is an Afon Arth, a 'Bear River.' There was a headland fort overlooking the estuary of this river.  Three Arto- 'Bear' names are found in the Ceredigion princely line only a few generations down from Ceredig.  The Welsh frequently link Arthur (from Roman Artorius) to their word for bear, 'arth.'  Furthermore, we know that the military unit serving at Segontium (not far from Dinas Emrys) was sent to Illyricum.  Dalmatia of the Salona Artorii and of Lucius Artorius Castus, who took three British legionary detachments to Armenia, was in Illyricum.  According to Roger Tomlin, it is possible some of these men retired and returned home to Segontium, perhaps bringing the name Arthur with them.  Lastly, the Segontium insignia was two crossed snakes, and this may have resurfaced in part of the story of the two snakes at Dinas Emrys.  Interestingly, the Uther elegy poem mentions a Pen Mynydd, and this is probably that place on Anglesey, where we find a dragon story that duplicates in several respects the Dinas Emrys tale. 

9) The battles of Arthur in the Historia Brittonum can be shown to be battles found in the Anglo-Saxon Chronicle.  I have worked these all out in detail. 

10) In the Life of St. Germanus of Auxerre, a British chieftain whose name can be related to the Elesa, father of Cerdic, in the ASC, has a boy whose crippled knee is described in such a way as to suggest an etiological development derived from a fanciful interpretation of the name Artorius/Arthur (cf. L. artus, arthritis). Elesa was not actually the father of Cerdic, of course, and the name is thought by scholars who have studied the AS genealogies to be an import (see Aloc, etc.).  However, Elafius in the VITA means 'stag, hart' in Greek, and Ceredig son of Cunedda has a son named Hyddwyn (from hydd, stag, hart).  The Gewissei pedigree in the ASC is reversed from what we find in the Welsh.

There is more, of course, but those are the most salient points, I feel.