The Sun is Central, the Moon surpassing;
The brightness, fearful, is eclipsed.
Historically, very little is really known concerning King Arthur. The Quest of the Holy Grail states that Arthur lived around 450AD. Historians call this time in English history the "Dark Ages" and England was known as the "Isle of the Dead" because for many centuries, Great Britain had very little contact with the literate society of Europe. A leader of Romanized Britons is documented as leading the resistance against the Anglo-Saxons around 600AD. These Britons wore armor and fought in a way that could leave legends behind them.1 That is the generally accepted time of Arthur if there was such a person. The Welsh believe in him and believe in his return in the same way the Indians of Mexico are longing for Quetzalcoatl. Galahad being made into the Christ of second coming is another example of a subject people waiting for their redeemer.
1 Churchill, Winston S. The Birth of Britain; Bantam Books; 1956.