Constantine the Great

The Roman Emperor Constantine (c. 280 - 337 A.D.) was one of the most influential personages in ancient history. By adopting Christianity as the religion of the vast Roman Empire, he elevated a once illegal cult to the law of the land. At the Council of Nicea, Constantine settled Christian doctrine for the ages. And by establishing a capital at Byzantium, laterConstantinople, he set into motion a series of events that would break the empire, split the Christian church and impact European history for a thousand years.

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https://www.thoughtco.com/constantine-the-great-112492