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Christianity Became the State Religion

Theodosius I and the Edict of Thessalonica

After many years of persecution at the hands of the Roman authorities, Christianity became the Roman empire’s sole state religion through the Edict of Thessalonica as decreed by the emperor Theodosius I (along with co-emperor Gratian). This is recorded on the Bible Timeline with World History at 380 AD.

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Theodosius I was born in Gallaecia region of the province of Hispania, a place where Christianity was embraced early in the faith’s history. His father, a successful military officer who served in Britannia and Mauretania, was executed in Carthage after the death of the emperor Valentinian I and as a result, the younger Theodosius was forced to return to Gallaecia. He redeemed himself after many years of service to the empire. Theodosius was elevated to co-emperor by Gratian when the Western Roman ruler Valens was killed in the Battle of Adrianople. Theodosius, then, took over the empire as sole emperor when Gratian died in 383 AD.

Three years before Gratian’s death, Theodosius (along with his co-emperors) proclaimed that the empire would not have any other religion other than Christianity. The years that led to 380 AD were tumultuous for Theodosius as he struggled to counter the Goths who settled in the Danube frontier. On February 27, 380, the emperors Gratian and Theodosius agreed to issue the Edict of Thessalonica or the Cunctos populos which endorsed Nicene Christianity as the state’s sole religion.

“St Ambrose Converting Theodosius”


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. According to the apostolic teaching and the doctrine of the Gospel, let us believe in the one deity of the Father, the Son and the Holy Spirit, in equal majesty and in a holy Trinity. 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. They will suffer in the first place the chastisement of the divine condemnation and in the second the punishment of our authority which in accordance with the will of Heaven we shall decide to inflict.


The edict was issued under the influence of Acholius, the Nicene bishop of Thessalonica, who, in turn, was influenced by Pope Damasus of Rome. This was a big improvement from Constantine the Great’s Edict of Milan which only legalized Christianity but tolerated paganism for many years. During this period, pagan temples were either shut or completely destroyed, such as in the case of the magnificent pagan temple in Edessa and the Serapeum in Alexandria. Paganism was not the only casualty of Theodosius’ zeal for Nicene Christianity—the believers of Arianism, branded long ago as heretics during the time of Constantine, were also suppressed and prohibited from public worship. Later in the same year, Theodosius removed Arian bishops from their positions in Constantinople which led to the gradual decline of Arian influence in the empire. The Niceno-Constantinopolitan Creed was adopted one year later by the First Council of Constantinople which was also assembled by Theodosius I.

Pierre SubleyrasWeb Gallery of Art:   Image  Info about artwork, Public Domain,
Errington, R. M. Roman Imperial Policy from Julian to Theodosius. Chapel Hill: University of North Carolina Press, 2006.
MacCulloch, Diarmaid. Christianity: The First Three Thousand Years. New York: Viking, 2010.
“Vol. Ip348 Chapter XI.” J. B. Bury: History of the Later Roman Empire • Vol. I Chap. XI. Accessed June 21, 2016.*.html.
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3 thoughts on “Christianity Became the State Religion

  1. I love this artical

  2. This is helpful and I love it.

  3. I love this. It makes me to know a little about how the catholic church came about. So in reality Christianity started with the church of christ.

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