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380-395 CEPrimary source · 2 sourcesWell documented

Theodosius Makes Christianity Mandatory, Then Rome Splits in Two for Good

On the timeline · around 380-395 CE · Decline & FallDecline & FallTheodosius Makes Christianity Mandatory, Then Rome Splits in Two for Good325 CE350 CE375 CE400 CE425 CE450 CE

What happened

On 27 February 380 CE, Theodosius I, ruling jointly with western emperors Gratian and Valentinian II, issued the decree known as Cunctos populos, usually called the Edict of Thessalonica. It ordered that Rome's subjects follow the Nicene form of Christianity, that only its followers could call themselves Catholic Christians, and that other Christian groups were heretics subject to punishment, going well beyond Constantine's earlier legalization of Christianity decades before, which had simply made the religion permitted. Theodosius reunited the eastern and western halves of the empire under his own rule, the last time this happened. When he died in 395 CE, the empire was divided between his two young sons, Arcadius in the east and Honorius in the west, and it was never reunified again.

Why it matters

This is the last moment in Roman history when one person ruled the whole empire. Every emperor after 395 CE ruled only an eastern or western half. The two halves then diverged sharply: the Western Empire collapsed within about 80 years, with the last western emperor deposed in 476 CE, while the Eastern Empire, which historians call the Byzantine Empire from this point onward, survived for roughly another thousand years until Constantinople fell in 1453.

How we know

The text of the Edict of Thessalonica survives because it was copied into the Theodosian Code, a compiled collection of imperial laws, and that text is preserved and translated in university sourcebook collections drawing on it. The succession of Arcadius and Honorius after Theodosius's death is recorded in contemporary chronicles and confirmed by the two men's own subsequent, separately dated coinage and laws issued from Constantinople and Ravenna, showing two genuinely separate administrations from that point forward.

Sources

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Part of a timelineAncient Rome30 events · From a legendary fratricide on the Palatine Hill to a teenage emperor's quiet deposition twelve centuries later, told through the battles, plagues, and one bridge-crossing that ended a republic.View all →
Theodosius Makes Christianity Mandatory, Then Rome Splits in Two for Good · Ancient Rome · SourcedStory