How Christianity moved from the margins of Roman society into the centre of imperial power

When Constantine died in 337 CE, the Roman Empire had entered a new age. Christianity had gained unprecedented imperial support, Constantinople had emerged as a new centre of power, and the government of Rome had become more centralized than it had been during the old Republic. Yet Constantine's death did not bring political stability. His sons inherited an enormous empire, but they also inherited the same problems that had troubled Roman rulers for generations. The question of who should rule remained dangerous, the army remained deeply involved in politics, and religious disagreements were becoming increasingly connected with imperial authority.

The Roman Empire had survived the Crisis of the Third Century by transforming itself. Diocletian had strengthened the bureaucracy, reorganized the provinces and introduced the Tetrarchy. Constantine had defeated his rivals, established a new imperial capital and changed the relationship between the Roman state and Christianity. But neither emperor had permanently solved the problem of succession. The Roman political system still depended heavily on the strength, alliances and military support of individual rulers.

Constantine's sons were Constantine II, Constantius II and Constans. After their father's death, the empire was divided among them and other members of the imperial family were eliminated in a violent struggle for control. The surviving brothers eventually divided the empire between themselves. Constantine II controlled territories in the west, Constans ruled Italy, Africa and parts of the western provinces, while Constantius II controlled the eastern empire.

This division was not yet the permanent separation of the Roman Empire into two independent civilizations. Roman emperors had divided authority many times before. The empire remained one political world in theory, and emperors continued to communicate, legislate and compete across its different regions. However, the eastern and western halves were developing increasingly distinct political and economic characteristics.

Constantius II eventually became the dominant ruler after the deaths of his brothers. He spent much of his reign dealing with military threats and religious disputes. The eastern frontier remained threatened by the Sasanian Empire, while the Rhine and Danube frontiers required constant military attention. At the same time, Christianity itself was divided over questions of theology.

The disputes that had emerged before the Council of Nicaea did not disappear after the council. Instead, they became more complicated. Bishops and Christian communities disagreed about the relationship between God the Father and Jesus Christ, and different emperors supported different theological positions. Some Christians supported the Nicene formulation, while others supported positions associated with Arius or other theological traditions.

The controversy became a remarkable example of how religion and imperial government had become connected. In earlier centuries, Christian communities had largely operated outside imperial political structures. Now emperors could call councils, support particular bishops and influence religious policy. Christian leaders, meanwhile, had to decide how they should respond to imperial involvement in matters of faith.

The result was not immediate religious unity. Instead, the fourth century became one of the most intellectually and politically active periods in Christian history. Councils were held, theological arguments spread between cities, bishops were removed from office and emperors repeatedly changed their policies. Christianity was becoming more powerful, but power also brought new conflicts.

One of the most important figures in this period was Athanasius of Alexandria. He strongly defended the Nicene position and became involved in repeated confrontations with emperors and bishops who supported alternative theological views. He was removed from his position and exiled several times. His career demonstrates that becoming a religion supported by the empire did not make Christianity politically simple. Christian leaders could still oppose emperors, and emperors could still attempt to control Christian institutions.

At the same time, Christianity was spreading beyond imperial courts and major cities. Monasticism became an important development in Christian life. Men and women began withdrawing from ordinary society to pursue lives of prayer, discipline and spiritual devotion. This movement became particularly important in Egypt, Syria and other eastern regions.

One of the most influential figures in early Christian monasticism was Anthony of Egypt, who became famous for living a life of solitude in the desert. Stories about his spiritual struggles circulated widely and inspired other Christians. Monastic communities gradually developed around such figures, creating new forms of religious organization.

The growth of monasticism changed the Christian landscape. Christianity was no longer simply a religion of urban communities meeting in houses or churches. It was becoming a complex world containing bishops, priests, monks, nuns, theologians, wealthy patrons, ordinary families and communities spread across the empire.

Christian churches also became increasingly visible within Roman cities. Basilicas were constructed on a large scale, often supported by imperial officials or wealthy Christians. These buildings became centres of worship, charity, administration and community life. The physical landscape of Roman cities was gradually changing as Christian buildings became part of the urban environment.

Yet the older religious traditions of Rome did not disappear immediately. Temples dedicated to traditional gods continued to exist in many parts of the empire. Public ceremonies connected with older religions continued in different places, and many families maintained traditional religious practices. Religious change occurred unevenly across the empire.

The process became more complicated during the reign of Julian, who ruled from 361 to 363 CE. Julian had been raised within the Christian imperial family but later rejected Christianity and attempted to revive traditional Roman religious practices. Christian writers later called him Julian the Apostate. Julian attempted to strengthen traditional cults, reorganize pagan priesthoods and reduce some forms of Christian imperial privilege.

Julian's reign was brief. He died during a military campaign against the Sasanian Empire in 363 CE. His successors returned to policies more supportive of Christianity. The attempt to restore traditional religion therefore did not reverse the broader transformation that had taken place during the fourth century.

The next major stage came with the reign of Theodosius I. Theodosius became emperor of the eastern Roman Empire in 379 CE and later became ruler of the entire empire. His reign was particularly important for the development of Nicene Christianity.

In 380 CE, Theodosius issued the Edict of Thessalonica, which supported the Nicene form of Christianity and declared it the imperial religious standard. This was a major development, but it should not be misunderstood as the moment when every Roman citizen suddenly became Christian. Religious change remained gradual, regional and complicated.

Traditional religions did not disappear overnight, and Christian communities themselves continued to disagree. The imperial government increasingly favoured Nicene Christianity, however, and the political balance had changed permanently. The Roman state was no longer simply tolerating Christianity. It was increasingly identifying imperial legitimacy with a particular form of Christian belief.

The Council of Constantinople in 381 CE reinforced the Nicene position and addressed questions concerning the nature of the Holy Spirit. Together with the earlier Council of Nicaea, it became an important foundation for what later generations would recognize as Nicene Christianity.

The transformation of the empire was also visible in laws concerning religious practices. Some traditional sacrifices and religious activities came under increasing restriction. Temples and traditional religious institutions faced growing pressure, although the exact experience varied greatly from region to region. In some places old religious buildings continued to be used for generations, while in other places they were abandoned, converted or destroyed.

This period should not be imagined as a simple war between Christians and pagans in which one side suddenly defeated the other. Roman society contained many different religious identities, and people sometimes changed their beliefs gradually. Some families included members with different religious practices. Some traditional customs survived because they were deeply connected with local culture rather than simply with theology.

Christianity itself also became more diverse as it expanded. Different communities developed different traditions, languages and forms of worship. Greek was especially important in the eastern Mediterranean, while Latin became increasingly dominant in the western provinces. Syriac and other languages were also used by Christian communities.

The empire's enormous geographical size meant that Christianity developed differently from place to place. Alexandria became a major centre of Christian theology. Antioch developed its own intellectual and religious traditions. Jerusalem held enormous symbolic importance because of its association with the life and death of Jesus. Constantinople became increasingly important because of its position as the imperial capital. Rome retained its unique importance because of its association with the apostles Peter and Paul and its long political history.

As Christianity grew, bishops became increasingly important figures within urban society. They did not simply lead religious ceremonies. Bishops could oversee charitable institutions, organize food distribution, negotiate with government officials and represent communities during times of crisis. Wealthy Christians increasingly supported churches, monasteries and charitable activities.

This new Christian social world also changed ideas about charity. Roman society had always contained forms of patronage and public generosity, but Christian communities developed strong traditions of caring for widows, orphans, the poor and the sick. Wealthy Christians were encouraged to use their resources for religious and charitable purposes.

The Christianization of Roman society therefore involved more than replacing one set of religious beliefs with another. It gradually affected ideas about family, charity, morality, death, education and community responsibility. Christian writers increasingly criticized practices they considered immoral, while emperors introduced laws influenced by Christian ideas.

Yet Roman society remained deeply unequal. Slavery continued, wealth remained concentrated among elites and poverty remained widespread. Christianity did not immediately eliminate these institutions. Christian thinkers debated slavery and social inequality in different ways, while Christian households continued to own enslaved people.

The Roman army also remained essential. Christianity had not removed the need for military power. Roman soldiers continued to defend the frontiers, and emperors continued to wage wars against neighbouring powers.

One of the most dangerous enemies remained the Sasanian Empire. Founded by Ardashir I in the third century, the Sasanian state had replaced the Parthian Empire and created a powerful rival to Rome in the east. Roman and Sasanian rulers fought repeatedly over Armenia, Mesopotamia and frontier territories.

The eastern frontier was therefore a world of diplomacy as well as warfare. Treaties, marriages, hostage exchanges, trade and military campaigns all shaped relations between the two empires. Neither side was capable of simply eliminating the other. Their rivalry would continue for centuries.

Meanwhile, the Roman frontier along the Rhine and Danube was also changing. Peoples whom Roman writers collectively described as barbarians were living beyond the imperial borders, but these societies were not simply disorganized groups waiting to invade Rome. They included different communities with their own political structures, economies and rivalries.

Rome traded with these peoples, recruited some of them into the army and sometimes fought against them. Some groups settled within imperial territory and became part of Roman society. Others became enemies. The frontier was therefore a zone of interaction rather than an absolute wall separating two completely different worlds.

During the late fourth century, one of the most important developments occurred when the Huns moved westward and placed pressure on communities living near the Roman frontier. Groups such as the Goths sought entry into Roman territory. In 376 CE, large numbers of Goths crossed the Danube into the empire.

Roman authorities struggled to manage the settlement. Poor treatment, corruption and exploitation contributed to growing tensions. In 378 CE, the Goths defeated the Roman army at the Battle of Adrianople. The eastern emperor Valens was killed, and the Roman army suffered a major defeat.

Adrianople became one of the most significant military disasters of the late Roman period. Yet it did not destroy the empire. Theodosius eventually negotiated settlements with Gothic groups and incorporated many Goths into the Roman military system.

The events revealed both the strength and vulnerability of the empire. Rome could still raise armies, collect taxes and negotiate with powerful groups, but the movement of large populations across the frontier created challenges that required careful political management.

Theodosius died in 395 CE. His sons Arcadius and Honorius inherited the eastern and western portions of the empire. This division is traditionally remembered as the division of the Roman Empire into East and West. In reality, the empire had been divided administratively many times before, and people at the time did not necessarily see 395 CE as the birth of two completely separate civilizations.

Nevertheless, the division became increasingly significant. Arcadius ruled from Constantinople, while Honorius eventually established his court in the western empire, with Milan and later Ravenna becoming important imperial centres. Rome itself was no longer the regular residence of the western emperor.

The eastern empire possessed several major advantages. It contained wealthy cities, productive agricultural regions and important trade routes. Constantinople was heavily fortified and occupied an extraordinarily strategic location. The eastern government also possessed access to significant financial resources.

The western empire faced different pressures. Its tax base was generally smaller, its political leadership was often unstable and military commanders became increasingly influential. The western provinces also experienced repeated conflicts involving groups entering or settling within Roman territory.

But it would be wrong to say that the western empire suddenly collapsed in 395 CE. The western Roman government continued to function for generations. Roman armies remained active, taxes continued to be collected, laws continued to be issued and emperors continued to claim authority over the western provinces.

The fourth century therefore ended with a Roman world that was fundamentally different from the empire of Augustus. Christianity had become deeply connected with imperial government. Constantinople had become one of the most important cities in the world. The empire was administratively divided between eastern and western courts. New peoples were moving across imperial frontiers, while Roman armies continued to defend the empire.

The transformation was not complete, however. The empire remained Roman. Its laws, institutions, armies, cities and political traditions continued to connect its people. Christianity itself was still developing, and religious disagreements would continue to shape imperial politics.

The great irony of this period was that Rome had survived by changing. The empire that emerged from the third century crisis was more centralized, more bureaucratic and more openly connected with Christianity than the empire ruled by Augustus. Yet these same transformations created new tensions.

As the fifth century approached, the Roman world stood at another turning point. In the west, military commanders and federate groups would become increasingly important. In the east, Constantinople would grow into a powerful imperial centre capable of surviving challenges that would destroy western imperial authority.

The story of Rome was therefore moving toward one of the most dramatic transformations in human history. The Roman Empire would not simply disappear. Instead, different parts of the Roman world would experience very different futures.

The eastern Roman Empire would continue for centuries after the western imperial government disappeared. Its people would continue to call themselves Romans, its emperors would continue to claim Roman authority, and Constantinople would become the centre of a civilization that preserved and transformed Roman political and cultural traditions.

In the west, however, the fifth century would bring invasions, migrations, civil wars, economic pressures and the gradual weakening of imperial authority. Cities would change, political power would become more regional, and new kingdoms would emerge within territories that had once been governed from Rome.

The story was therefore not simply about the fall of Rome. It was about transformation. The Roman world was becoming something new, and the people living through it could not yet know what the future would bring.