Theodosius I: Last United Emperor and Christian Rome

Flavius Theodosius was appointed emperor of the East in January 379 CE by Gratian following the catastrophe of Adrianople (378 CE), where his predecessor Valens had been killed fighting the Visigoths. Rather than exterminating the Visigoths, Theodosius negotiated a settlement (382 CE) allowing them to settle as federated allies within the empire — the foederati system. The Edict of Thessalonica (380 CE) declared Nicene Christianity the only legitimate form of Christianity and the official religion of the Roman state. Paganism was addressed in edicts culminating in 391-392 CE: sacrifices were banned, temples closed, and access to pagan sanctuaries forbidden. The Olympic Games ended. The fire of Vesta, tended for over a thousand years, was extinguished. The Vestal Virgins were disbanded. He died in Milan in January 395 CE. The empire was divided between his sons: Arcadius (East) and Honorius (West). It would never be reunited.

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