Editing Pope Nicholas I (section)

===Relations with the Eastern Church===
In the East, Nicholas was seen as trying to extend his papal power beyond what was canonical authority by asserting a "rulership" over the Church instead of the position of "highest honor among equals" accorded to the pope of Rome by the East. He contended that [[Patriarch Ignatios of Constantinople]] was deposed in 858 and [[Photius I]] raised to the patriarchal see in violation of [[ecclesiastical law]].<ref name=O'Malley/> Nicholas sent two bishops as papal legates to the [[Council of Constantinople (861)|Council of Constantinople]] in 861, but they failed to follow papal instructions. In a letter of 8 May 862 addressed to the patriarchs of the East, Nicholas called upon them and all their bishops to refuse recognition to Photius, and at a Roman synod held in April 863, he excommunicated Photius.
[[File:The interrogation of Patriarch Photios.jpg|thumb|13th-century depiction of the interrogation of Photius I]]
According to the Church of Constantinople, Photius was elected lawfully and canonically by the will of the Byzantine Emperor [[Michael III]] in 858. This decision was affirmed later in 879 in a [[Fourth Council of Constantinople (Eastern Orthodox)|synod of Greek bishops]] regarded as ecumenical by some in the Orthodox Church. At this synod, Ignatius’ elevation to the patriarchate was declared to be uncanonical and Photius was acclaimed as properly elected as the new patriarch, a decision which ran counter to [[Fourth Council of Constantinople (Catholic Church)|a previous council held at Constantinople]] –  regarded as ecumenical by the Catholic Church – in which Photius had been deposed and Ignatius reinstated. The Eastern Church resented Nicholas' pressing of the doctrine of papal primacy. This led to conflict between Constantinople and Rome over doctrinal issues such as the addition of the [[Filioque clause]] to the [[Nicene-Constantinopolitan Creed]] and territorial claims due to the Church of Constantinople's seizure of territory from the Roman Patriarchate in southern Italy, Sicily and Illyricum during the [[Iconoclast controversy]]. A synod at Constantinople, headed by Photios,  in 867 excommunicated Nicholas{{sfn|Gallagher|2019|p=90}} and rejected his claims of primacy, his efforts to convert [[Bulgaria]] to the obedience of the Roman Church, and the addition of the Filioque clause in parts of the Latin Church. The news of excommunication did not arrive in Rome until after Nicholas' death.{{sfn|Gallagher|2019|p=90}}

For a variety of reasons, Prince [[Boris I of Bulgaria]] became interested in converting to Christianity and undertook to do that at the hands of western clergymen to be supplied by King [[Louis the German]] of [[East Francia]] in 863. Late in the same year, the Byzantine Empire invaded [[First Bulgarian Empire|Bulgaria]] as it suffered famine and natural disasters. Boris was forced to sue for peace. Because the majority of his people were still opposed to Christianity, he was secretly baptized according to the Byzantine rite. The Byzantine Emperor who became his godfather conceded territory in [[Thrace]] to him.

Unhappy with Byzantine influence and desiring an [[autocephalous]] status which Photius was unwilling to grant, Boris sent an embassy to Nicholas with 106 questions on the teaching and discipline of the Church in August 866. Nicholas answered these inquiries in his "''Responsa Nicolai ad consulta Bulgarorum''" ([[Giovanni Domenico Mansi]], "Coll. Conc.", XV, 401 sqq.) and sent missionaries under the papal legate bishop Formosus (later [[Pope Formosus]]). Also in 866, Nicholas sent a letter to the Bulgarians ordering the [[Book burning|burning of any books]] captured from the Muslims because they were deemed harmful and blasphemous.<ref>{{cite book|author1=Benjamin Z. Kedar|title=Crusade and Mission: European Approaches Toward the Muslims|date=14 Jul 2014|publisher=Princeton University Press|isbn=9781400855612|page=32}}</ref> When [[Pope Adrian II]] rejected Boris's request that either [[Formosus]] or [[Marinus I|Marinus]] be made [[archbishop of Bulgaria]], Boris began to look again towards Constantinople. In 870 a council of Constantinople granted the autocephalous status and Greek priests were sent as missionaries; they were soon replaced by Bulgarians.