Within British (and by that I mean Welsh/Cymry/Celtic) legend, a High Council–a Parliament of a sort–existed in the Dark Ages to choose a “high king”. One of these high kings, according to legend, was King Arthur. Later, during Arthur’s reign, he instituted his ’round table’, a gathering of equals, to discuss the troubles in his realm. Or so the story goes.
But did this High Council ever exist?
The answer is ‘yes’–certainly during the reign of the last Prince of Wales, Llywelyn ap Gruffydd. In 1282 when Edward I of England wrote his letters to Llywelyn and Dafydd, demanding that they concede defeat, he also wrote a letter to the ‘Council of Wales’, laying out his case. To this they responded:
“The people of Snowdonia for their part state that even if the prince desired to give the king seisin of them, they themselves would not do homage to any stranger, of whose language, customs and laws they are utterly ignorant. For by doing so they could be brought into perpetual captivity and barbarously treated . . .” http://garthcelyn.com/letters_14.html
Our evidence for a council of ‘Britain’ (which in the post-Roman occupation period did include all of what is now England and Wales) is first and foremost, Gildas. He writes: “Then all the council members, together with that proud tyrant [theoretically, Vortigern], were so blinded, that, as a protection to their country, they sealed its doom by inviting in among them (like wolves into the sheep-fold), the fierce and impious Saxons, a race hateful both to God and men, to repel the invasions of the northern nation.”
From Robert Vermaat: “What Gildas does not do is describe Vortigern as a sole ruler, or a ‘High King’ if you will. He rules as a king, but together with a Council, the members of which are rulers of their own territory. Gildas sees this as a logical but reprehensible evolution from the usurpation of Magnus Maximus, which has seen the progressive disintegration of the British territory from one single state (diocese) into several smaller kingdoms without overlord in Gildas’ day.
Though in the days of Vortigern this was clearly not the case, and Vortigern’s decisions seem to be obeyed in the whole diocese. Dumville has proposed that there is nothing to suggest that Vortigern’s rule did not encompass the whole diocese. But Vortigern is not ruling alone, as observed above. He has power over magistrates, who later evolve into sub-kings or provincial rulers, but that power may have been wielded by the Council as a whole, for Gildas puts the blame with all of them. Gildas does not mention the Council in this function elsewhere, or so it seems. Gildas does seem to indicate, however, that the members of the council in the days of Vortigern had become the warring princes of his own days.” http://www.vortigernstudies.org.uk/artsou/gildvort.htm
That a council of Britain existed appears to have been a common understanding throughout the subsequent centuries, as Geoffrey of Monmouth, writing in the twelfth century mentions it often. He states that Britains ‘flocked together from all parts and in a council held at Silchester,’ and crowned Constantine High King; furthermore, Aurelius holds a council in chapter 7 and 8 of book 6; and Arthur in chapter 1 and 16 of book 9.
Additional mention of some kind of council is found in the Chronicle of the Princes (Red Book of Hergest). From 1096: “And the Britons, having retreated to their strongest places, according to their usual custom, agreed in council to save Mona.”
Chronicle of the Princes (Ystrad Fflur). From 1220: “Llywelyn, prince of Gwynedd, gathered to him the princes and leading men of all Wales. . .”
1258: “In this year all the Welsh made a pact together, and they gave an oath to maintain loyalty and agreement together, under pain of excommunication upon whomsoever of them broke it.”
Certainly the power of the Council was not constant, and in part depended upon the unity of Wales as a whole and the individual authority of the ruling high king, and later Prince.
As to whether King Arthur was ever high king? At this point, we just don’t know.