Nicene Christianity became the official state religion of the Roman Empire in 380, when Emperor Theodosius I issued the Edict of Thessalonica. The following year he called the First Council of Constantinople, which formally adopted the Nicene Creed. Although the earlier Edict of Milan (313) had granted Christians religious toleration, the Edict of Thessalonica went further by giving Christianity official state support and elevating it above other religions practiced within the empire.
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