Well worth the wait. Thanks for such a thorough response!

The history of Christianity in the Roman Empire is a tricky one, especially as it is always subject to misconceptions (e.g. Constantine was the first “Christian” Emperor, Christianity ended the Roman Empire…. The list goes on and on). There is no particular date Christianity was officially adopted- and all the dates you have offered are reasonable choices. As I am meant to be writing my PHD proposal this evening, and really don’t want to, I will do my best to give an overview of how Christianity became the official religion of the Roman Empire. I warn you this answer has turned out a lot longer than I intended- there is a TL;DR at the end which answers your question as well!

Christianity was famously persecuted by the Romans and this is true… to an extent. There were persecutions of the Christians, notoriously Nero blamed them for the great fire of Rome. However, there were long periods where Christianity and the Roman Empire peacefully coincided- especially the “little peace” of the church from around 260-300 CE. However, this came to an abrupt end in 303 CE, when the Emperor Diocletian renewed persecution. Eusebius, an early and prominent church historian, tells us ‘It was in the nineteenth year of the reign of Diocletian […] that letters were published everywhere, commanding that the churches be leveled to the ground and the Scriptures be destroyed by fire’. The persecutions under Diocletian would later form an important part of the Christian consciousness, though they officially ended in 311 with an edict of toleration from Galerius.

However, sadly Galerius never gets much credit for this, because two years later (and after another civil war, for which the Roman’s were so famous) Constantine became joint emperor with Licinius, and they published a new edict of toleration. This was effectively just confirming what had already been said by Galerius previously, and was basically asserting that the new rulers would maintain the same laws, but all the same the Edict of Milan as it was known, has become erroneously famous for ending the persecution of the Christians, and legalising the religion. It is important to note that the Edict of Milan did not give Christianity any special privileges, it said churches were not to be taxed, but this was the case for any religious institution in Rome, and it restored to Christian’s the property lost in the Diocletianic persecution.

And this brings us onto Constantine, one of my personal favourite historical figures, and a man whose religion has been the source of so much debate. Constantine has been largely remembered for being the “First Christian Emperor”, and while there are arguments on both sides, its not a title I think very much deserved. He certainly approved of Christianity, and worshiped the Christian God, but the extent to which he saw Christianity as fundamentally different from any other religion at the time, particularly the god Sol Invictus, is very much up for debate. I will try not to go into too much speculation here, and will mainly focus on how Constantine did welcome Christianity into the empire, but as one of my lecturers put it last year ‘Constantine’s religion was Constantine’.

In 312, Constantine was fighting a rival claimant for the throne, Maxentius, and the night before a battle, was reported to have had a vision of the Christian symbol the Chi-Rho in the sky, and heard a voice saying ‘By this sign Conquer’. Subsequently, Constantine ordered his army to paint the Chi-Rho on their shields, and they went on to win a victory.

Constantine and Licinius then decreed the Edict of Milan in 313, and in 314 Constantine became the first Roman Emperor to call a Church council. In North Africa, there was conflict between the “Catholics” and a sect of Christians known as the Donatists (this conflict was rooted in Diocletian’s persecutions- which did have a really big impact on Christianity) and to resolve the issue, Constantine called the Council of Arles, which ultimately condemned the Donatists. Arles itself hasn’t left a massive mark on History, but it’s successor, the Council of Nicaea, did.

After a bit more civil war, Constantine became sole Emperor in 324. And in 325, apparently sick of all the arguing amongst the Christians, called the Council of Nicaea, over which he himself presided. Nicaea laid out some of the fundamental tenets of the church, the Apostolic Creed, which is still read in churches today, was agreed upon and the Arian heresy was officially condemned (though it would persist for a long time). Ultimately, between the Council of Arles and the Council of Nicaea Constantine had set a vital precedent: a connection between the church and the Roman state which would persist for over a millennia, and paved the way for Christianity becoming the official religion of Rome.

Constantine dies in 337, and is succeeded by his three sons, Constantius II, Constantine II and Constans (Because the Constantinian dynasty was very original when it came to choosing names). All three sons are Christians, and for the next twenty-odd years Rome has Christian emperors, who rule over both the Christian and Pagan populations of the empire. Whilst the fourth century sees a lot of prominent churchmen who would go on to shape Church history, including Athanasius, Ambrose and Jerome, it was also filled with pagan authors and figures. Ammianus Marcellinus is one of the more prominent examples, an ex-soldier who wrote the Res Gestae, which lamented the state of decline of Rome, and thought Christians probably had something to do with it. He partially pins the blame of the Roman loss at the Siege of Amida for example, on the Christian general Sabinianus spending too long at martyrs’ tombs in Edessa, rather than joining the battle.

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