5.8 — How Christianity Conquered an Empire

Around 30 CE a Jewish preacher from Galilee was executed by the Roman governor of Judaea, by a method reserved for slaves, rebels and the lowest criminals. His movement at that moment consisted of a few dozen frightened people in a provincial backwater.

Three hundred years later the emperor was a Christian. Within another sixty years it was the empire's official religion and the old temples were closing.

This chapter is about how that happened, treated as history. It does not attempt to settle theological claims — Volume VII takes the traditions seriously on their own terms. What can be examined historically is the movement, its growth, and the political process by which its doctrines were fixed.

What we can and cannot know about the founder

On the historical Jesus, the mainstream position among historians, including non-religious ones, is that a Jewish teacher of that name was baptised by John the Baptist and was crucified under Pontius Pilate. These two events are considered best attested, partly because they are awkward for the later movement to explain — a criterion historians call embarrassment, on the reasoning that a tradition does not invent difficulties for itself.

The sources are the problem. The gospels were written roughly 40 to 70 years after the events, by believers, in Greek, for communities with particular concerns, and they disagree with each other on details. Non-Christian references are brief: Tacitus mentions Christus executed under Pilate; Josephus mentions the movement, in a passage that has been partly altered by later Christian copyists in a way that is generally agreed; Pliny the Younger writes to the emperor asking how to handle Christians in his province.

What this book does is describe the movement, where the evidence is much better.

Why it grew

The early growth rate is not mysterious once it is quantified. The sociologist Rodney Stark's calculation is instructive: starting from around a thousand Christians in 40 CE, a growth rate of about 40 percent per decade — roughly 3.4 percent a year — produces around six million by 300 CE, which matches the historical estimates. That is a rate ordinary religious movements achieve today. No mass conversions are needed; the arithmetic of compounding does it.

But something has to drive the compounding, and several factors did.

1. It was open to everyone, and it said so. Roman religion was tied to cities, families and ethnic groups. Judaism required substantial commitment and, for men, circumcision. Christianity, after the decision recorded in Acts and argued out by Paul, dropped the requirement that converts become Jews first, and admitted anyone regardless of ethnicity, sex, status or citizenship. That decision — reached in a dispute in the movement's first two decades — is the single most consequential organisational choice in its history.

2. It offered something to people at the bottom. Slaves, women, the urban poor and foreigners had no meaningful place in civic religion. Christianity offered them full membership, a defined moral status, and a community that would bury them properly.

3. Practical care, which is the most-documented factor. Christian communities fed widows, supported orphans, ransomed captives and cared for the sick. During the plagues of the second and third centuries, when many fled the cities, Christians stayed and nursed people. Simple nursing — food, water, keeping the sick warm — substantially raises survival rates in epidemic disease. So Christians survived better, their patients survived better, and the survivors owed their lives to them. The emperor Julian, trying to revive paganism in the 360s, wrote in frustration that the "impious Galileans" support not only their own poor but ours as well, and that this shames the traditional cults.

4. Women. Christianity attracted proportionally more women than men, and this compounds. It forbade infanticide, which in the Roman world was disproportionately practised on female infants, and it disapproved of abortion, which was dangerous to the mother. A community with a more balanced sex ratio and a higher birth rate grows faster. Christian women also married non-Christians and often converted the household.

5. The martyrs. Persecution was intermittent rather than constant — most of the time Christians were ignored — but under Decius from 250 CE and Diocletian from 303 CE it was systematic. Public executions of people who refused to save themselves by a trivial act of sacrifice were, on the evidence, persuasive rather than deterrent. Tertullian's line that the blood of the martyrs is the seed of the church is propaganda that seems to have been broadly accurate.

6. Organisation. By the third century there was a structure — bishops in each city, deacons handling charity, letters circulating between communities, agreed lists of authoritative texts developing, and a system for readmitting those who had lapsed under persecution. It was the best-organised voluntary association in the empire.

Constantine

In 312 CE, before the battle of the Milvian Bridge, Constantine adopted a Christian symbol for his troops and won. The accounts of a vision come from Christian writers, one of them decades later and drawing on Constantine's own recollection.

What he actually did matters more than what he believed. In 313 CE the Edict of Milan granted toleration to all religions and restored confiscated Christian property. He then favoured the church heavily: tax exemptions for clergy, funding for basilicas, jurisdiction for bishops in certain civil cases, and imperial attention to church disputes.

Three corrections to the popular account.

He did not make Christianity the official religion. That was Theodosius I in 380 CE, nearly seventy years later, who made Nicene Christianity the state religion and subsequently banned pagan sacrifice.

He did not compile the Bible. The canon developed over centuries through use and argument, with the list matching the modern New Testament first appearing in a letter of Athanasius in 367 CE and being confirmed at later councils.

And he did not invent the doctrine of Christ's divinity at Nicaea, which is a persistent claim. What Nicaea did in 325 CE was settle a dispute between Arius, who held that Christ was created by and subordinate to the Father, and Athanasius, who held that Christ was of the same substance. Both sides were arguing about how Christ is divine, not whether. The council decided for Athanasius, and the losing position — Arianism — persisted for centuries and was the form of Christianity most Germanic peoples adopted, which is why the Goths and Vandals ruling Roman provinces were religiously at odds with their subjects.

What Constantine unquestionably did was change the incentives. After 313 CE, being a Christian went from dangerous to advantageous. Conversion rates rose steeply, and the quality of conviction certainly fell — a complaint made loudly at the time, and a major reason the monastic movement began, as people seeking a serious version withdrew to the desert.

Doctrine decided by council and by politics

This is the part usually left out, and it is important for understanding how religions actually develop.

The councils — Nicaea 325, Constantinople 381, Ephesus 431, Chalcedon 451 — were assemblies of bishops, convened and often chaired by emperors, deciding contested questions by argument and vote, with imperial power then enforcing the result. Losing parties were exiled and their books burned.

The disputes were about genuinely difficult questions. How can one God be three persons? How can one person be both fully divine and fully human? These are not trivial and the arguments were serious, but they were settled in an environment where imperial politics, regional rivalry between the great sees of Rome, Alexandria, Antioch and Constantinople, and personal power struggles all bore on the outcome.

And the losers did not vanish. The churches that rejected Chalcedon in 451 — in Egypt, Ethiopia, Syria and Armenia — still exist. The Church of the East, which rejected Ephesus, spread east along the Silk Roads (Chapter 5.7) into Persia, Central Asia, India and China, and the Syrian Christians of Kerala belong to that tradition, with a community that long predates any European presence in India.

One point deserves emphasis for an Indian reader. Christianity in India is not a colonial import. The Saint Thomas Christian community of Kerala traces itself to the first century, and there is documented contact with the Church of the East from at least the fourth, with a settled community, its own bishops and its own liturgy, centuries before Vasco da Gama arrived. Chapter 8.4 covers what happened when the Portuguese found them and tried to bring them under Roman authority.

Why the church outlived the empire

When the western imperial administration failed (Chapter 5.5), the church was the only institution left that spanned the former empire.

It had a structure — bishops in every city, a hierarchy, and communication between them.

It had literacy. Monasteries copied texts, including classical ones, and the clergy were the only reliably literate group for centuries.

It had property and income, having accumulated substantial landholdings.

It had legitimacy independent of any king, deriving from a source no local ruler controlled.

So bishops took over functions the state had dropped — feeding the poor, negotiating with invaders, organising defence, running courts. Pope Leo I is recorded as meeting Attila the Hun in 452 CE and persuading him to turn back, whatever the actual reasons were.

And the monasteries became the west's institutional memory. Benedict's rule, written around 530 CE, prescribed a balanced day of prayer, work and reading, and required monasteries to have libraries. Almost every classical Latin text that survives does so because monks copied it, and Chapter 7.4 follows what that made possible.

Where this shows up in your life

The calendar. Dating from the supposed birth of Christ was devised by a monk, Dionysius Exiguus, in 525 CE, and became standard slowly. He was probably off by a few years. The seven-day week with a rest day, and the whole festival calendar of the Christian world, come from here (Chapter 15.1).

The hospital and the university. Both grew from church institutions — hospitals from monastic infirmaries and the church's obligation to care for the sick, and universities from cathedral schools (Chapter 7.4).

Charity as an institution. The idea that a religious community should systematically support the poor of the wider society, not only its own, is one of the movement's genuine innovations, and Chapter 4.8's Axial ethics is where its roots lie.

And the general mechanism is worth extracting, because it applies to every religion in this volume. A movement's beliefs are one thing; what makes it grow is usually organisation, community, care for members, an open door, and enough time for compound growth. Then, when it acquires state power, its doctrine gets fixed by committees under political pressure, and the versions that lose become minorities or heresies. Chapter 7.1 shows a very similar sequence with Islam, and Chapter 8.7 shows the whole thing coming apart again in the Reformation.

What Part 5 established

Greece invented citizen self-government, deductive proof and natural explanation, and used them alongside slavery and empire. Alexander destroyed Persia in a decade and built nothing, but the Greek-speaking world his successors created became the medium through which India, Persia and the Mediterranean exchanged ideas for centuries. Rome invented the idea of turning defeated enemies into citizens, conquered the Mediterranean, and destroyed its own republic in the process — and then built a law, an infrastructure and an administrative model that outlived it everywhere. Han China ran a comparable empire on a completely different principle and, unlike Rome, kept reassembling itself. And a religion travelling those trade roads outgrew and then absorbed the empire that had executed its founder.

What the next Part covers

Volume VIII now turns to India and stays there for twenty-eight chapters. Part 6 begins with the land itself — the mountains, rivers, coasts and rainfall that decided where Indians could live, farm, trade and be invaded — and then runs the whole story: the Vedic age and what the evidence actually says about it, the sixteen kingdoms and the Buddha, the Mauryas, the Guptas, the great southern empires most syllabi skip, the Sultanate, the Mughals with both sides of their ledger, the Marathas and the Sikhs, why India kept losing to smaller forces, how a trading company took a subcontinent, what colonial economics really did, 1857, the freedom movement in all its streams, Gandhi and Nehru on the documented record, Partition with its accounting, and the long argument about why a country with this much talent is still called developing.