Priestess of Avalon is a 2000 novel by American writer Marion Zimmer Bradley, completed posthumously by Diana L.

[1] It follows detailing the life of Helena, first wife of Western Roman Emperor Constantius Chlorus and mother of Constantine.

The Roman noble takes her away from Avalon as she is banished for this forbidden love and, before long, Helena bears him a son, who will become Constantine the Great.

As Empress-Mother, Helena travels on a pilgrimage to the Holy Land to find the answers to questions that arise between the old religion and the new.

Publishers Weekly praised the novel, and wrote that "Paxson's own skill at bringing historical characters and places to vivid life enriches Helena's story.