He was the first Christian Roman emperor. He reversed the persecutions of his predecessor, Diocletian, and issued the Edict of Milan in 313, which proclaimed religious tolerance of Christians throughout the empire.
The foremost general of his time, Constantine defeated the emperors Maxentius and Licinius during civil wars. He also fought successfully against the Franks, Alamanni, Visigoths, and Sarmatians during his reign.
He even resettled parts of Dacia which had been abandoned during the previous century. Constantine also transformed the ancient Greek colony of Byzantium into a new imperial residence, Constantinople, which would be the capital of the Eastern Roman Empire for over one thousand years. He died on 22 May 337 (aged 65) in Nicomedia (modern-day Izmit, Turkey).
If you want to know more about him, you must visit: Constantine the Great, (274-337)