Christianity as the Roman state religion

In the year before the First Council of Constantinople in 381, Christianity became the official religion of the Roman Empire when Theodosius I, emperor of the East, Gratian, emperor of the West, and Gratian's junior co-ruler Valentinian II issued the Edict of Thessalonica in 380,[1] which recognized the catholic orthodoxy[a] of Nicene Christians as the Roman Empire's state religion.

A series of ecumenical councils convened by successive Roman emperors met during the 4th and the 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the theological and christological doctrines of Arianism, Nestorianism, Miaphysitism, and Dyophysitism.

The early Muslim conquests of the 7th–9th centuries would begin a process of converting most of the then-Christian world in the Levant, Middle East, North Africa, regions of Southern Italy and the Iberian Peninsula to Islam, severely restricting the reach both of the Byzantine Empire and of its church.

[citation needed] Justinian I, who became emperor in 527, recognized the patriarchs of Rome, Constantinople, Alexandria, Antioch, and Jerusalem as the supreme authorities in the state-sponsored Chalcedonian church apparatus (see the Pentarchy).

However, Justinian claimed "the right and duty of regulating by his laws the minutest details of worship and discipline, and also of dictating the theological opinions to be held in the Church".

[14][15] With the crowning of Charlemagne by Pope Leo III on 25 December 800 as Imperator Romanorum, the political split between East and West became irrevocable.

Spiritually, Chalcedonian Christianity persisted, at least in theory, as a unified entity until the Great Schism and its formal division with the mutual excommunication in 1054 of Rome and Constantinople.

[22][23][24] Since paying taxes had been one of the ways that Jews demonstrated their goodwill and loyalty toward the empire, Christians had to negotiate their own alternatives to participating in the imperial cult.

Their refusal to worship the Roman gods or to pay homage to the emperor as divine resulted at times in persecution and martyrdom.

[40] Constantine began to utilize Christian symbols such as the Chi Rho early in his reign but still encouraged traditional Roman religious practices including sun worship.

In the early 4th century, a group in North Africa, later called Donatists, who believed in a very rigid interpretation of Christianity that excluded many who had abandoned the faith during the Diocletianic Persecution, created a crisis in the western empire.

However, during the reign of Emperor Julian the Apostate, the Donatists, who formed the majority party in the Roman province of Africa for 30 years,[43] were given official approval.

[citation needed] On 27 February of the previous year, Theodosius I established, with the Edict of Thessalonica, the Christianity of the First Council of Nicaea as the official state religion, reserving for its followers the title of Catholic Christians and declaring that those who did not follow the religion taught by Pope Damasus I of Rome and Pope Peter of Alexandria were to be called heretics:[46] It is our desire that all the various nations which are subject to our Clemency and Moderation, should continue to profess that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition, and which is now professed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic holiness.

We authorize the followers of this law to assume the title of Catholic Christians; but as for the others, since, in our judgment they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give to their conventicles the name of churches.

[citation needed] By the time Christianity became the state religion of the empire at the end of the 4th century, scholars in the West had largely abandoned Greek in favor of Latin.

Rejection of the Council of Chalcedon led to the exodus from the state church of the majority of Christians in Egypt and many in the Levant, who preferred Miaphysite theology.

[39] By 476, the Germanic chieftain Odoacer had conquered Italy and deposed the last western emperor, Romulus Augustus, though he nominally submitted to the authority of Constantinople.

[39] In 533, Roman Emperor Justinian in Constantinople launched a military campaign to reclaim the western provinces from the Arian Germans, starting with North Africa and proceeding to Italy.

Justinian definitively established Caesaropapism,[53] believing "he had the right and duty of regulating by his laws the minutest details of worship and discipline, and also of dictating the theological opinions to be held in the Church".

"[54] By the end of the 6th century the church within the Empire had become firmly tied with the imperial government,[55] while in the west Christianity was mostly subject to the laws and customs of nations that owed no allegiance to the emperor.

[12] Emperor Justinian I assigned to five sees, those of Rome, Constantinople, Alexandria, Antioch and Jerusalem, a superior ecclesial authority that covered the whole of his empire.

[74] During the 9th century, the Emperor in Constantinople encouraged missionary expeditions to nearby nations including the Muslim caliphate, and the Turkic Khazars.

Of these, the Church in Great Moravia chose immediately to link with Rome, not Constantinople: the missionaries sent there sided with the Pope during the Photian Schism (863–867).

In Serbia, which became an independent kingdom in the early 13th century, Stephen Uroš IV Dušan, after conquering a large part of Byzantine territory in Europe and assuming the title of Tsar, raised the Serbian archbishop to the rank of patriarch in 1346, an autonomy recognized in 1375 by Constantinople,[79] a rank maintained until after the fall of the Byzantine Empire to the Turks.

This church became independent only in 1448, just five years before the extinction of the empire,[82] after which the Turkish authorities included all their Orthodox Christian subjects of whatever ethnicity in a single millet headed by the Patriarch of Constantinople.

In the East, the idea that the Byzantine emperor was the head of Christians everywhere persisted among churchmen as long as the empire existed, even when its actual territory was reduced to very little.

[89] The church had come to merge psychologically in the minds of the Eastern bishops with the empire to such an extent that they had difficulty in thinking of Christianity without an emperor.

[21] In Western Europe, on the other hand, the idea of a universal church linked to the Emperor of Constantinople was replaced by that in which the Roman see was supreme.