When people think of the first centuries of the Roman Empire, they imagine a crowded religious marketplace: temples to Jupiter, processions for Isis, secret gatherings of Mithraists, ecstatic festivals for Cybele. Against this backdrop, Christianity sometimes gets cast as “just another mystery religion.” But the evidence — both Christian and pagan — tells a different story.

Christianity grew in ways no other religion did. And it grew because it was different.

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A Movement That Could Not Be Ignored

By the year AD 112, the Roman governor Pliny the Younger wrote to Emperor Trajan about the rapid spread of Christianity in his province of Bithynia-Pontus:

“For many persons of every age, every rank, and also of both sexes are and will be endangered. For the contagion of this superstition has spread not only through the cities but also through the villages and the countryside.”
— Pliny, Letters 10.96 (Loeb Classical Library), written c. AD 112

Pliny’s words confirm what the New Testament had already claimed: Christianity wasn’t staying local. It had spread across cities, villages, farms, households, men and women, slave and free. This was no longer a tiny sect in Jerusalem — it was a movement Rome could not ignore.

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Growth by the Numbers

Sociologist Rodney Stark, in The Rise of Christianity (1996), famously calculated that Christianity expanded at about 40% per decade — slow and steady exponential growth. Bart Ehrman, in The Triumph of Christianity (2018), adopts a similar model for illustration.

• 30 AD: a few dozen disciples in Jerusalem
• 100 AD: ~7,000–10,000
• 200 AD: ~200,000–300,000
• 300 AD: ~4–6 million
• 350 AD: ~30 million (roughly half the empire)

No other religion in antiquity shows a comparable curve.

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Why Was Christianity Different?

1. Exclusivity

Roman religion was inclusive. You could worship Mithras in the army, Isis at home, and Jupiter in the forum. Christianity, by contrast, insisted that all other gods were false. Converts had to abandon sacrifices and festivals. Romans accused them of being “atheists” for rejecting the gods of the empire.

Judaism shared that exclusivity, but it was ethnic and national. Christianity took it further: one God for all nations.

Justin Martyr, writing in the mid-2nd century (c. AD 155), put it this way:

“We do not sacrifice to idols, for we know they are not gods but lifeless and dead. We do not worship with the multitude, but we direct prayers to the only true God.”
— Justin, First Apology 9 (Loeb/ANF)

Later in the 2nd century, Tertullian sharpened the same point in legal and political terms. Accused of disloyalty to the emperor, he replied:

“We Christians are accused of being irreligious with regard to the emperors. But let it be said: we do not worship the emperor, we will not swear by the genius of Caesar. We worship him lawfully, as a man, and pray for him. But as for the gods, we know that they are no gods.”
— Tertullian, Apology 24 (written c. AD 197, Loeb/ANF)

That phrase — “we worship him lawfully, as a man” — is carefully chosen. Christians would:

• Honor the emperor in his human role (by paying taxes, obeying laws, and praying for him).
• But they would not cross into idolatry by offering sacrifices or calling him divine.

This was the flashpoint of exclusivity. Christians were loyal citizens in every human way — but their refusal to honor the gods (and Caesar’s genius) made them appear dangerous, even atheistic, to Roman society.

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2. Universality

Other cults were tied to particular groups: Mithraism to soldiers, Isis to Egyptian traditions, Cybele to Asia Minor. Christianity declared itself for everyone.

Paul put it in striking terms:

“There is neither Jew nor Greek, there is neither slave nor free, there is no male and female; for you are all one in Christ Jesus.”
— Paul, Letter to the Galatians 3:28 (written c. AD 50s, Loeb/NRSV)

Nearly a century later, Justin Martyr could make the same claim even more boldly:

“There is no people, whether Greek or barbarian, or any race whatsoever, among whom prayers and thanksgivings are not offered through the name of the crucified Jesus.”
— Justin, First Apology 46 (written c. AD 155, Loeb/ANF)

From Paul to Justin, the message is consistent: Christianity was not a local or ethnic faith. It was a movement that claimed universality — open to all nations, classes, and peoples.

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3. Community and Care

This is where Christianity truly stood apart. Roman society had structures of family, guilds, and even associations — but none looked like the Christian ethic of charity.

• Roman families (familia) cared for their own household, but responsibility rarely extended beyond kin and slaves.
• Guilds and burial clubs (collegia) sometimes pooled resources for funerals, but their reach was limited and local.
• Philosophical schools (Stoics, Epicureans, Platonists) spoke of virtue and brotherhood in theory, but offered no system of daily material support to the poor.
• Mystery cults like Isis or Mithras provided rituals and camaraderie, but not hospitals or famine relief.

Christianity was different. Caring for widows, orphans, the poor, the sick, and even strangers was commanded as part of the “way of life” (Didache 1–4, c. AD 80–100).

During the plague of the 260s, Dionysius of Alexandria described the difference Christians made:

“Most of our brethren, in their exceeding love and brotherly kindness, did not spare themselves, but kept by each other, and visited the sick without thought of danger, and ministered to them assiduously, and treated them for their healing in Christ, and with them departed this life serenely happy; for they were infected by others with the disease, drawing upon themselves the sickness of their neighbors, and willingly taking over their pains.”
— Eusebius, Ecclesiastical History 7.22 (Loeb Classical Library, written c. AD 310–325, quoting Dionysius’s letter from c. AD 260)

Even pagan critics noticed. Lucian of Samosata, a satirist writing around AD 170, mocked Christians for their enduring practice of brotherhood:

“The poor wretches have convinced themselves, first and foremost, that they are going to be immortal and live for all time… and then it was impressed on them by their original lawgiver that they are all brothers from the moment they are converted, and deny the gods of Greece, and worship that crucified sophist himself, and live under his laws. So they despise all things indiscriminately and consider them common property.”
— Lucian, The Passing of Peregrinus 13 (Loeb Classical Library, written c. AD 170)

And this care extended to the most vulnerable: children. In Roman society, it was common to expose unwanted infants — especially girls — leaving them to die or be taken as slaves. Philosophers like Aristotle endorsed the practice. But Christians condemned it as murder and became known for rescuing and raising exposed infants.

The Epistle of Barnabas (c. AD 130) instructed believers:

“You shall not kill a child by abortion, nor shall you destroy it after birth.”
— Barnabas 19.5 (Loeb, Apostolic Fathers)

This was radical. Christians didn’t only nurse plague victims — they took in abandoned babies, treating them as precious image-bearers of God.

And later, even Rome’s own emperor admitted it. Julian the Apostate (who tried to revive paganism after Constantine) begrudgingly confessed:

“Why do we not observe how it is their benevolence to strangers, their care for the graves of the dead, and the pretended holiness of their lives that have done most to increase atheism [i.e., Christianity]?”
— Julian, Letter to Arsacius (Loeb Classical Library, written c. AD 362)

Julian even instructed pagan priests to imitate Christian charity — because he knew it was winning hearts.

So while families cared only for their own, guilds helped only with burials, and philosophers offered only ideals, Christians made charity the center of their identity. This ethic reshaped communities across the empire.

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4. Moral Demands

Pagan cults emphasized ritual. Christianity demanded a transformed life.

Pliny himself noted that Christians bound themselves by oath:

“They asserted, however, that the sum and substance of their fault or error had been that they were accustomed to meet on a fixed day before dawn and sing responsively a hymn to Christ as to a god, and to bind themselves by oath, not to some crime, but not to commit fraud, theft, or adultery, not to falsify their trust, nor to refuse to return a trust when called upon to do so.”
— Pliny, Letters 10.96 (Loeb Classical Library, written c. AD 112)

For Christians, morality wasn’t optional — it was central.

And Christian writers pointed to transformed lives as the greatest proof of all. Origen, writing in the mid-3rd century, argued:

“Their reform of life is the strongest testimony that they have come upon a truth that cannot be shaken. For who that sees the untold multitudes who have abandoned their former vices, and given themselves to a pure and sober life, does not wonder at the power that has wrought this change?”
— Origen, Against Celsus 1.67 (written c. AD 248, Loeb)

For Origen, the very existence of morally changed communities was itself evidence that Christianity was real and divine.

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5. A Historical Resurrection

Skeptics sometimes argue that the resurrection of Jesus was just another version of the “dying and rising god” myths in the ancient world. But when we examine the actual stories, each one is different in crucial ways — especially when it comes to dates and eyewitnesses.

Osiris (Egyptian):

• Date: 2nd millennium BC; Plutarch, On Isis and Osiris (c. AD 100).
• Story: Murdered, dismembered, reassembled, becomes ruler of the underworld.
• Eyewitnesses: None.
• Difference: Never returns bodily to life among mortals.

Dionysus (Greek):

• Date: 6th c. BC (Homeric Hymns); 4th c. BC (Orphic).
• Story: Torn apart, restored; fertility cycles.
• Eyewitnesses: None.
• Difference: Cyclical vegetation rebirth, not historical resurrection.

Attis (Phrygian):

• Date: 4th–3rd c. BC cult; Roman references 1st c. BC–4th c. AD.
• Story: Castrates himself, dies under a tree; later myths say preserved from decay.
• Eyewitnesses: None.
• Difference: Mourning cult, not resurrection.

Adonis (Greek/Near Eastern):

• Date: 7th–6th c. BC cult; Ovid Metamorphoses (AD 8); Lucian (AD 150).
• Story: Killed by boar; blood gives flowers; seasonal return.
• Eyewitnesses: None.
• Difference: Fertility myth.

Inanna/Ishtar (Mesopotamian):

• Date: Descent of Inanna (c. 1750 BC); Descent of Ishtar (7th c. BC).
• Story: Dies in the underworld, restored by gods.
• Eyewitnesses: None.
• Difference: Cosmic myth, not history.

Romulus (Roman):

• Date: Legendary founder, 8th c. BC; Livy, History of Rome 1.16 (27–9 BC); Plutarch, Life of Romulus (c. AD 100).
• Story: Competing endings — (1) vanishes in a storm; (2) Proculus Julius claims vision; (3) Senators murdered him and invented tale.
• Eyewitnesses: One vision, contradictory stories.
• Difference: Apotheosis (becoming divine), not bodily resurrection.

Heracles (Greek):

• Date: Homer (8th c. BC); Apollodorus (1st–2nd c. AD).
• Story: Dies on pyre; mortal part destroyed, divine part ascends.
• Eyewitnesses: None.
• Difference: Apotheosis, not resurrection.

Zalmoxis (Thracian):

• Date: Herodotus, Histories 4.94–96 (c. 440 BC).
• Story: Hides underground for three years, reappears.
• Eyewitnesses: Followers saw him reemerge, but he never died.
• Difference: Retreat-and-return, not resurrection.

Melqart (Phoenician):

• Date: Cult at Tyre, 9th c. BC; Greek accounts 5th c. BC onward.
• Story: Annual rites of seasonal renewal.
• Eyewitnesses: None.
• Difference: Fertility ritual, not resurrection.

Mithras (Roman cult):

• Date: Late 1st c. AD in Rome.
• Story: Slays bull; Mithras never dies.
• Eyewitnesses: None.
• Difference: No resurrection myth at all.

Apollonius of Tyana (Greek philosopher):

• Date: 1st c. AD; Philostratus, Life of Apollonius (c. AD 217–238).
• Story: Three endings — (1) dies in Ephesus; (2) dies in Lindus; (3) vanishes in Crete, appears to one disciple.
• Eyewitnesses: At most, one disciple in one version; others contradict.
• Difference: Late, legendary, contradictory; no bodily resurrection.

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Why Christianity Was Different

By contrast, the Christian proclamation was unique:

• Early: The resurrection was proclaimed from the very start. Paul’s letters (c. AD 50s) are our earliest Christian writings, but in 1 Corinthians 15:3–7 he cites a creed he himself “received” from the Jerusalem church — most scholars date this creed to within five years of Jesus’ death (c. AD 30–35).
• Historical: Located in Jerusalem under Pontius Pilate. Tacitus (c. AD 115) confirms: “Christus, the founder of the name, was put to death by the procurator Pontius Pilate, during the reign of Tiberius.” — Annals 15.44 (Loeb)
  Even atheist or agnostic historians today agree on three facts: Jesus lived, was crucified under Pilate, and his followers soon claimed to see him alive.
• Eyewitnessed: Paul lists appearances:
  1. To Cephas (Peter)
  2. To the Twelve
  3. To more than five hundred at once (most still alive when Paul wrote)
  4. To James (the brother of Jesus)
  5. To all the apostles
  6. Finally, to Paul himself
     Plus, we have four independent Gospels (Matthew, Mark, Luke, John, AD 65–95), each preserving distinct traditions but united in testifying to Jesus’ crucifixion, burial, and resurrection.
• Bodily: Jesus left behind an empty tomb and ate with disciples; not a ghost, not apotheosis.
• Transformative: These claims produced communities whose lives of charity and moral transformation astonished even critics.

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Conclusion

Christianity wasn’t “just another mystery religion.”

• It was exclusive like Judaism, but universal in scope.
• It demanded moral transformation, not just ritual.
• It built enduring communities of care unmatched in Roman society — nursing plague victims, rescuing exposed infants, treating every life as sacred.
• And it proclaimed not a seasonal myth or apotheosis, but a historical resurrection, rooted in eyewitness testimony and confirmed by transformed lives.

By AD 300, Christians numbered in the millions. By AD 350, they were half the empire. What began as a small sect in Jerusalem became the movement that reshaped the world.