Pope Joan, A Novel by Donna Woolfolk Cross

Suspend for a moment the belief that a woman could never be Pope and you will enjoy this “historical” fiction. The novel is filled with descriptions of the dark ages (A.D. 814) including war, plague, Vatican intrigue and politics, and the status of women.
Joan is born in a Frankland village to a Saxon mother and an English father. Joan is very bright and is taken under the wing of a Greek scholar. Ultimately, she takes the place of a younger brother at a Benedictine monastery when he is killed by Saxon invaders. She thrives in the learned environment dressed as a man and then moves to Rome where her wisdom and medical skills allow her to outshine her peers.
Although, “she leads a man's life, Joan dies a woman's death, losing her life in childbirth. In this colorful, richly imagined novel, Cross ably inspires a suspension of disbelief…” Publishers Weekly 2006.

You can read more about Pope Joan at the following websites:
http://abcnews.go.com/Primetime/Story?id=1453197&page=1
http://en.wikipedia.org/wiki/Pope_Joan
http://www.usnews.com/usnews/doubleissue/mysteries/pope.htm
http://wais.stanford.edu/Religion/religion_FirstFemalePope(110503).html
And in this book at Helen Hall Library:
The Myth of Pope Joan by Alain Boureau.