Pope Nicholas I reigned from
858 to
867, and is remembered as a consolidator of Papal authority and power. He refused to grant an annulment to
Lothar II from Theutberga so that Lothar could marry his mistress Waldrada; when a Council pronounced in favor of annulment Nicholas I declared the Council to be deposed, its messengers excommunicated, and its decisions void. Despite pressure from the Carolingians, who laid siege to Rome, his decision held. During his reign relations between Rome and Constantiople soured over the appointment of
Photius as Patriarch.
Successor of Pope Benedict III
Succeeded by Pope Hadrian II[?]