In 858, fifteen years after the triumph of icons under Theodora, Photius became the Patriarch of Constantinople. He has been termed the most distinguished thinker, the most outstanding politician, and the most skillful diplomat ever to hold the office of Patriarch. Soon after his accession he became involved in a dispute with Pope Nicolas I (858-67). The previous Patriarch, Ignatius, had been exiled by the Emperor and while in exile had resigned under pressure. The supporters of Ignatius, declining to regard this resignation as valid, considered Photius a usurper. When Photius sent a letter to the Pope announcing his accession (the long-held custom was that churches would inform others when new patriarchs were chosen – they never asked permission). Nicolas decided that before recognizing Photius he would look further Into the quarrel between the new Patriarch and the Ignatian party. Accordingly in 86i he sent legates to Constantinople.
Photius had no desire to start a dispute with the Papacy. He treated the legates with great deference, inviting them to preside at a council in Constantinople, which was to settle the issue between Ignatius and himself. The legates agreed, and together with the rest of the council they decided that Photius was the legitimate Patriarch. But when his legates returned to Rome, Nicolas declared that they had exceeded their powers, and he disowned their decision. He then proceeded to retry the case himself at Rome: a council held under his
presidency in 863 recognized Ignatius as Patriarch and proclaimed Photius to be deposed from all priestly dignity. The Byzantines took no notice of this condemnation and sent no answer to the Pope’s letters. Thus an open breach existed between the Churches of Rome and Constantinople.
The dispute clearly involved the Papal claims. Nicolas was a great reforming Pope, with an exalted idea of the prerogatives of his see, and he had already done much to establish an absolute power over all bishops in the west. But he believed this absolute power to extend to the east also: as he put it in a letter of 865, the Pope is endowed with authority over all the earth, that is, over every Church. This was precisely what the Byzantines were not prepared to grant. Confronted with the dispute between Photius and Ignatius, Nicolas thought that he saw a golden opportunity to enforce his claim to universal jurisdiction: he would make both parties submit to his arbitration.