The reason Canon 10 was established is due to the fact that layman Photius usurped the office of Patriarch of Constantinople from the rightful Patriarch Ignatius.

Ignatius was arrested and exiled to the island of Terebinthos in 858, where he submitted his resignation.

Pope Nicholas felt that the appointment needed the consent of Rome and objected to the fact that Photius was a layperson even though there was precedence for this in both the Western and Eastern churches. He also demanded that the Byzantines give back to Rome the territories of Calabria and Sicily

In 861, with approval of Photius, Emperor Michael convened a general council in the Church of the Holy Apostles, known as the First-Second Synod. The pope was invited, and he was glad to send his delegates. He sent them with the instruction to investigate the election of Photius in relation to the canons and and to demand that Illyricuм and southern Italy be given to Rome. This synod ratified the actions of the Seventh Ecuмenical Council condemning iconoclasm. Also, Photius was affirmed as the lawful and canonical patriarch.

When the delegates returned to Rome and that Nicholas found that his demands for territorial rights were not considered, he became angry and excommunicated his delegates. He convened a council in Rome in 863 in which he deposed and excommunicated Photius on the basis that his appointment was uncanonical. He chose to recognize Ignatius as the legitimate patriarch.

The legates of Pope John VIII attended, prepared to acknowledge Photius as legitimate patriarch, a concession for which the pope was much censured by Latin opinion