In the 9th Century, 'Joan the English' pulled off what is potentially one of the greatest con-tricks in history. Dressed as a man, she tricked her way into the papacy and reigned for over two years before being discovered - when she gave birth in the street. 

Despite evidence of some 500 medieval writers, the Catholic Church claim that Joan is nothing but a protestant invention. If she did exist, it raises serious questions about the Catholic ban on women in the Church. Peter Stanford investigates.