who made christianity the official religion of rome

Christianity was made the official state religion of the Roman Empire by Emperor Theodosius I through the Edict of Thessalonica in 380 CE, issued together with the Western emperors Gratian and Valentinian II.

Quick Scoop

• Theodosius I, ruling the Eastern Roman Empire, declared Nicene Christianity the only legitimate imperial religion in 380 CE with the Edict of Thessalonica.

• This edict recognized the form of Christianity defined by the Council of Nicaea as the faith all Roman subjects were expected to follow, branding other Christian groups as heretical.

• Earlier, Emperor Constantine had only legalized Christianity and ended persecution with the Edict of Milan in 313 CE; he did not make it the official state religion.

How it unfolded

• 313 CE: Constantine issues the Edict of Milan, granting Christians legal status and religious freedom but keeping traditional Roman cults in place.

• 380 CE: Theodosius I, with Gratian and Valentinian II, issues the Edict of Thessalonica, declaring Nicene Christianity the official religion of the Empire.

• After 380 CE: Pagan temples are increasingly closed and non‑Nicene Christian groups lose legal protection and property, cementing Christian dominance.

Key names to remember

• Theodosius I (“the Great”) – the emperor most directly responsible for making Christianity the official state religion of Rome via the Edict of Thessalonica.

• Gratian and Valentinian II – Western co‑emperors who co‑signed the edict, extending its force across the whole Empire.

• Constantine the Great – first Roman emperor to convert to Christianity and to legalize and promote it, laying the groundwork but stopping short of making it the state religion.

Information gathered from public forums or data available on the internet and portrayed here.