EN
The unstable circumstances in Byzantium due to the differences between the ecclesiastical and political powers and the immediate ordination and election of Photios to the throne of Patriarch of Constantinople, gave the pope of Rome Nicholas I the chance to make claims over ecclesiastical issues. His non‑canonical interventions, the missions imposing Latin customs and language in services, with the patriarchate of Constantinople in Bulgaria and Moravia at the same time, along with the doctrine of “filioque” led Photios to call the Synod of Constantinople (879 – 880), thus putting an end to the pretensions of the popes and preventing the imminent schism between East and West. The deeper causes that led to the increasing dissension between the East and West and finally to the schism in 1054 are analysed in the survey by means of the source material founded in the work of Photios.