Mists of Avalon by Marion Zimmer Bradley
This is one of my favorite books based on the King Arthur legend. What I really like about it is the story is told from the point of views of the women in Arthur’s life, which gives us a different perspective. This is mostly a fantasy tale with magic, focusing on the mysterious Isle of Avalon. The Mists of Avalon's Camelot politics and intrigue take place at a time when Christianity is taking over the island-nation of Britain; Christianity vs. Faery, and God vs. Goddess are dominant themes. Highly recommended.
Kelley Heckart, Historical fantasy romance author