In Arthurian Romance, the Isle of Avalon is the Christianised form of the Summer Land in Celtic mythology. Instead of an Otherworld, it became an actual place, in the county of Somerset.

The Celtic goddess Morrigan became Morgan le Fay, who was called "the royal virgin of Avalon". Unlike the Christian Heaven, Avalon was a place of adventure and ulimited possibilities.

The Summer Land was perpetually in the month of May. Apple trees bore both fruit and flower at the same time. All kinds of flowers could be found. Young men and women lived together without shame. Nobody ever got angry, ill, or old. No one has any personal possessions and everything was shared.

It was like a shangri-la of the Middle Ages. Avalon was thought to be a mysterious island, where King Arthur aboded with the nine sisters. Morgan was the most skilled of the sisters, with the ability to heal, shape-shift, and fly.

The Rival of the goddess Morgan is Guinevere, "the flower bride" or "May Queen". As a spring goddess, she is fought over by the Lords of Summer and Winter. The Knight Gawain says of Guinevere:

"Just as the wise master teaches young children, my lady the queen teaches and instructs every living being. From her flows all the good in the world, she is its source and origin. Nobody can take leave of her and go away disheartened, for she knows what each person wants and the way to please each according to his desires."

Thus we can see that the pursuit of the Knights was for the lost Goddess, in hiding from the Roman Church. The goddess was also called the "Holy Grail", and to find her was to restore the Summer Land to the world.