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Which Christian creed did Theodosius I support?

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Theodosius I supported the Nicene Creed, which asserts that Jesus Christ is of the same substance as God the Father.1

In his efforts to establish religious unity within the empire, Theodosius issued an edict on February 28, 380, that mandated this belief for all his subjects, defining those who accepted the consubstantiality of the Father, Son, and Holy Spirit as Catholic Christians. He subsequently directed the convening of the First Council of Constantinople in 381, which officially sanctioned the Niceno-Constantinopolitan Creed—a development of the original creed from the First Council of Nicaea—as the universal norm for Christian orthodoxy. Through these actions, he vigorously suppressed Arianism and solidified the Trinitarian doctrine as the foundation of the state-supported faith.123