The legend of a female Pope is just that, a legend. From Larousse's Dictionary of World Folklore (via "Pope Joan--Legendary female pontiff, said to have reigned as John VIII from 855 to 858 until her male disguise was exploded by labour pains. In fact Benedict III succeeded Leo IV in 855 after a period of only a few weeks.

"One of the earliest forms of the legend is found in the 13th century 'De septum donis Spiritu Sancti' ('The Seven Gifts of the Holy Spirit') by Stephen of Bourbon; according to him Joan was elected pope in Rome in c. 1100 after showing extraordinary learning as a scribe and notary, but upon giving birth during a papal procession to the Lateran Church her imposture was discovered and she was taken out of the city and stoned to death. Later accounts claimed that she died in childbirth during the procession, and it was said that subsequent popes avoided that street in their own papal processions. She was often known as Agnes or Gilberta or simply remained anonymous until the name Joan became the standard form in the 14th century.

"The most influential source for the legend was Martin of Troppen, a 13th-century Dominican, who named her as Johannes Angelicus, born of English parents in Mainz, and set the date of her election at 855. She disguised herself as a man to follow her beloved to Athens, where she trained. The legend was accepted as historical for many centuries, and seized upon by Protestant reformers in the 16th and 17th centuries, but after the 18th century the myth began to lose credibility. It has been suggested that the fable may have originated from satiric criticism of the influential female senator Marozia in 10th century Rome."

Another detail found in some versions of the legend is that supposedly all Popes since then have had to sit in a chair with a hole in the seat and have some other Church representative stick a hand through the hole, feel their genitals, and announce "Testiculos habet" ("he has testicles"). This ceremony does not really occur either.