Like many tales of "manipulative" historical significance, any
negative aspects of Arthur's (who WAS a good leader of men)
"supernatural" supporters (underworld beings without a doubt,
as they belonged to the realm of "faerie") are played down. But
the content is obvious, and has been repeated many times, in
terms of manipulation of human cultures, history, and politics.
The pre-Saxon legends which preceded the Arthurian cycle, and
upon which they are largely based, are in the Welsh
MABINOGION. One of the heroes, who is an Arthur-like
character, is Pwyll Prince of Dyfed, who journeys at will into
Annwn or the underworld in search of a wife. This woman,
Rhiannon, is similar in many respects to Nimue and may in fact
represent the same underworld queen. And yes, Annwn IS the
underworld. The original pre-medieval tales about Arthur himself
are in the MABINOGION as well.
--Mike