Additional sources

http://www.holyspiritinteractive.net/columns/guests/patrickmadrid/popejoan.asp

"In the history of the popes, there is no place where this legendary figure will fit in."

Leo IV was pope from 847 till July 17th 855. The coronation of Benedict III took place on 29th September of the same year and he lived till 858. There is no room for a John Anglicus (John English) to have reigned for 2 1/2 years between. This period of history is well documented and the succession of Benedict III within a few months of Leo's death is well attested.

Encyclopedia Brittannica:

http://www.britannica.com/EBchecked/topic/304201/Pope-Joan

Chronicles predating Martin Polonus that allude to "Pope Joan":

Liber Pontificalis by Anastasius in the 9th century ((HT 12)).
Historiographi by Marianus Scotus of 1083 ((HT 12)).
The Chronographia of Sigeburt of Gemblourx, 1105-1112 ((HT 12)).
A History of the Popes by Bishop Otto of Frisingen, 1146 ((HT 12)).
A History by Richard of Poitiers of 1172 ((HT 12)).
The Pantheon by Gotfrid of Viterbo, about 1186 ((HT 12)).
A History by Gervase of Tibury in 1214 ((HT 12)).

In all these cases the earliest manuscripts fail to mention a woman pope. It is only in editions produced some time after 1275 that she appears.


Historically, Protestants and atheists have also generally rejected the myth.

http://atheism.about.com/od/popesandthepapacy/a/popejoan.htm
http://www.usnews.com/usnews/doubleissue/mysteries/pope.htm