Constantine I 307-337 AD Thessalonica, 312-313 AD, Reduced Follis, 3.40g.

Constantine I^[g] (Latin: Flavius Valerius Constantinus; 27 February c. 272 – 22 May 337), also known as Constantine the Great, was a Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity.^[h] He played a pivotal role in elevating the status of Christianity in Rome, decriminalizing Christian practice and ceasing Christian persecution in a period referred to as the Constantinian shift.^[4] This initiated the Christianization of the Roman Empire. Constantine is associated with the religiopolitical ideology known as Caesaropapism, which epitomizes the unity of church and state. He founded the city of Constantinople and made it the capital of the Empire, which remained so for over a millennium.

Born in Naissus, in Dardania within Moesia Superior (now Niš, Serbia), Constantine was the son of Flavius Constantius, a Roman army officer of Illyrian origin who had been one of the four rulers of the Tetrarchy. His mother, Helena, was a Greek woman of low birth, probably from Asia Minor in modern Turkey. Later canonised as a saint, she is traditionally credited for the conversion of her son. Constantine served with distinction under the Roman emperors Diocletian and Galerius. He began his career by campaigning in the eastern provinces (against the Persians) before being recalled in the west (in AD 305) to fight alongside his father in the province of Britannia. After his father's death in 306, Constantine was proclaimed as augustus (emperor) by his army at Eboracum (York, England). He eventually emerged victorious in the civil wars against emperors Maxentius and Licinius to become the sole ruler of the Roman Empire by 324.