Leo IV, pope from 847 to 855, was a Roman by birth, and was unanimously chosen to succeed Sergius II. His pontificate was chiefly distinguished by his efforts to repair the damage done by the Saracens during the reign of his predecessor to various churches of the city, especially those of St Peter and St Paul. It was he who built and fortified the suburb on the right bank of the Tiber still known as the Civitas Leonina -- the Leonine City. A frightful conflagration, which he is said to have extinguished by his prayers, is the subject of Raphael's great work in the Sala dell'Incendio of the Vatican.

He held three synods, one of them in 850, distinguished by the presence of Louis II, but none of them otherwise of importance. The history of the papal struggle with Hincmar of Reims, which began during Leo's pontificate, belongs rather to that of Nicholas I. Benedict III was Leo's immediate successor. However, some believe the female Pope Joan succeeded him, disguising herself as a man; however, Joan is generally believed to be fictitious.

original text taken from the 9th edition (1882) of the Encyclopædia Britannica