Rome became Christian gradually, not all at once. The key milestones were 313 CE , when Constantine legalized Christianity, and 380 CE , when it became the official state religion under Theodosius I.

Quick Scoop

If you mean when Rome stopped persecuting Christians , the answer is 313 CE.

If you mean when Christianity became the official religion of the Roman Empire , the answer is 380 CE.

What happened

  • 312–313 CE: Constantine’s conversion and the Edict of Milan ended official persecution and legalized Christianity.
  • 325 CE: The Council of Nicaea helped organize Christian doctrine across the empire.
  • 380 CE: The Edict of Thessalonica made Nicene Christianity the official state religion.

Short answer

So, the simplest answer is: Rome became Christian in stages, with legal acceptance in 313 CE and official state status in 380 CE.

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Milestone Date Meaning
Legalization of Christianity 313 CE Christians were no longer officially persecuted and could worship openly
Official state religion 380 CE Nicene Christianity became the Roman Empire’s official religion