Constantine the Great

~272–337 CE · Roman (Naissus, modern-day Serbia) · Late Roman Empire

Known for: First Christian emperor—legalized Christianity and founded Constantinople

Constantine won a brutal civil war to become sole emperor, then made the most consequential religious decision in Western history: legalizing Christianity through the Edict of Milan (313 CE). He claimed to have seen a vision of the cross before his decisive victory at the Milvian Bridge.

He convened the Council of Nicaea (325 CE), which defined core Christian doctrine, and moved the empire's capital to Byzantium—renamed Constantinople—creating a new Rome that would last 1,100 years as the Byzantine Empire.

He was baptized only on his deathbed, suggesting either pragmatic hedging of bets or a genuine belief that last-minute baptism washed away a lifetime of murder (he killed his own son Crispus and wife Fausta under mysterious circumstances).

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