By 250 CE the Christian Church was under severe pressure. The Roman Empire was collapsing, and many Romans believed that the embrace of Christianity by many members of their upper classes had contributed to this unwelcome development. The new Emperor Decius was one such Roman and set out to recover what he saw as Rome's "Golden Age," a glorious chapter in her history in which the pagan gods had smiled down upon the great city on the Tiber.
Not long after becoming emperor, Decius published an edict requiring everyone in the Empire except Jews to carry out sacrifices to the Roman gods. Inevitably, Christians found themselves unable to comply with the emperor's edict on pain of idolatry. At that point in time, Christianity had grown considerably, taking advantage (ironically) of the Roman Empire's extensive trade routes to spread its message. Christians were no longer part of a minor cult which could easily be marginalized or contained. They could indeed be persecuted, but it would require a much greater effort on the part of the Roman authorities to ensure full compliance with their edict than in previous years.
Inevitably, perhaps, the so-called Decian Persecution was unable to check the spread of Christianity. Though brutal in places, the edict was only arbitrarily enforced within the empire. Some Christians, mainly out of fear, applied for a certificate to prove they had carried out the appropriate sacrifices. However, most did not, and the bonds of solidarity between Christians, if anything, strengthened. In fact, by 251 CE, at the end of the Decian Persecution, the church was still in remarkably good shape overall with a large number of practicing clergy still in existence in Rome, despite the death of Pope Fabian in prison.
The Church was also thriving in North Africa, and it was here that the first great figures of Christian theology emerged. Origen, for instance, utilized Greek learning to formulate the first truly systematic Christian theology. He also adopted a highly original method of biblical exegesis, using both allegorical as well as literal methods of interpretation. Origen's novel synthesis of biblical teaching with pagan philosophy proved controversial in subsequent years, and his work was condemned at the Second Council of Constantinople in 553 CE.
In contrast, another great North African theologia, Tertullian, famously asked the rhetorical question, "What has Athens to do with Jerusalem?" meaning that Christianity could stand on its own two feet as a coherent system of teaching without the aid of pagan thought. But on the whole, Christian theology was heavily influenced by Greek philosophy in this period. Paul had many years before embarked upon a widespread program of evangelization throughout the pagan world, and it became necessary from a practical standpoint to proclaim the Christian message in a recognizable form. Henceforth, the question wasn't whether pagan thought should influence Christian theology, but to what extent.
The Church continued to grow apace under the benign reign of Emperor Gallienus. He restored Roman tolerance to the Christian faith, largely for reasons of imperial stability and social peace. As well as growing in number, Christians were able to become more fully integrated into Roman society. The character of the Christian faith continued its gradual development from an heretical Jewish cult to a separate and distinct religion. As Christianity spread, it became culturally more Hellenistic and less Hebraic. Many of its most prominent ecclesiastics had converted directly from paganism to Christianity, bringing with them their Greek culture and learning. The church had now been almost completely severed from its Jewish origins.
Yet the status of Christianity remained unsteady. So long as the church was dependent on the whim of a Roman emperor for its survival, it could never feel truly secure. And so it proved. In 303, Diocletian began a systematic persecution of Christians throughout the empire. But the campaign of persecution, though widespread, was not uniformly carried out. Diocletian was simply one of four ruling emperors, two of whom (Constantius and Maximian) were unwilling participants in the general proscription. And so the Church, though considerably weakened, lived on to fight another day.
It seemed to many Christians that the Church would only enjoy any degree of long-term stability if it had access to temporal as well as spiritual power. Thankfully, they wouldn't have too long to wait. At the Battle of Milvian Bridge in 312, Constantine, son of Constantius, claimed to have a vision promising him victory against his rival, the Emperor Maxentius, if his soldiers had the Chi-Ro symbol (☧) painted on their shields. Whatever the veracity of this story, there can be no doubt that Constantine credited Christianity with his victory on the battefield that day. And the rest, as they say, is history.
The Christian Church now had what it had needed for a long time: temporal power to buttress its spiritual authority. The rise of Christianity from an obscure offshoot of Judaism to a world religion was now complete. The Emperor Constantine set about reversing the effects of Diocletian's persecution, formally promulgating the Edict of Milan in 313 CE. Not only was Christianity now tolerated, it was actively encouraged, even favored within the empire.
In addition, Constantine took on the role of an arbiter in theological disputes. The persecutions under Diocletian had been particularly harsh in North Africa. This had led to the explosion of a number of heretical Christian sects, such as the Donatists, who held that any clergyman who had yielded to persecution under the Romans was indelibly corrupted and could no longer administer the sacraments. Christianity, they felt, should be a church of saints, not sinners.
Another live theological issue was the question of the Trinity. Controversially, the ascetic Arius held that Christ was a subordinate member of the Trinity, somehow less than God the father. Arius believed that there was a time when Jesus had not existed, that he came after the Father. Christian orthodoxy, however, insisted that he was co-equal and co-eternal with God the Father.
By 325, the debate was becoming increasingly bitter. As Christianity was now effectively the state church of the Empire, theological disputes inevitably had political repercussions. So it became necessary for Constantine to convene a Church Council to try and resolve the matter. The setting for this monumental task was Nicaea. Constantine presided over the Council's deliberations, so there was always considerable pressure on the delegates to come to an agreement as soon as possible. It soon became clear to all concerned that the acquisition of temporal power by Christianity had been bought at the cost of theological diversity. In truth, the final outcome was never in any serious doubt. Constantine wanted stability in his empire and made it clear that he desired an outcome in keeping with anti-Arian orthodoxy.
The Council banished Arius and sent a number of his followers into exile. The ensuing statement of theological intent, the Nicene Creed, re-asserted the consubstantiality of the Father and the Son. But Arianism had not been vanquished or anything like it. It still lived on with remarkable persistence in various parts of the empire, particularly North Africa. And it would be quite some time before the Arian heresy was extirpated completely.
The Christian Church had come a long way since the Decian Persecution. It was continuing to grow rapidly right throughout the empire; it had a better-educated, more professional clergy; it enjoyed a much greater sense of stability thanks to its alliance with the temporal power of the Roman imperium; and it had developed a more sophisticated theology, conceived largely as a means of reaching out to converts in the pagan world. In the centuries to come, Christianity would continue to develop further, encountering various trials and tribulations along the way. But the years from 250 to 350 CE represented a kind of baptism of fire for the Church, a period of myriad challenges and setbacks from which it emerged stronger and more resilient than ever. An important chapter in the history not just of Christianity but of the world had been turned. And there was to be no going back.