Eastern Roman Empire (Byzantine Empire) / Emperors Constantine the Great, Constantine II and Constantius II

Constantine the Great (Latin: Flavius Valerius Aurelius Constantinus Augustus Greek: Κωνσταντῖνος ὁ Μέγας), also known as Constantine I or Saint Constantine (in the Orthodox Church as Saint Constantine the Great, Equal-to-the-Apostles), was a Roman Emperor from 306 to 337 AD.

Constantine was the son of Flavius Valerius Constantius, a Roman army officer, and his consort Helena. His father became Caesar, the deputy emperor in the west in 293 AD. Constantine was sent east, where he rose through the ranks to become a military tribune under the emperors Diocletian and Galerius. In 305, Constantius was raised to the rank of Augustus, senior western emperor, and Constantine was recalled west to campaign under his father in Britannia (Britain). Acclaimed as emperor by the army at Eboracum (modern-day York) after his father's death in 306 AD, Constantine emerged victorious in a series of civil wars against the emperors Maxentius and Licinius to become sole ruler of both west and east by 324 AD.

Constantine is a significant figure in the history of Christianity. The Church of the Holy Sepulchre, built on his orders at the purported site of Jesus' tomb in Jerusalem, became the holiest place in Christendom. The Papal claim to temporal power in the High Middle Ages was based on the supposed Donation of Constantine. He is venerated as a saint by Eastern Orthodox, Byzantine Catholics, and Anglicans.

Between 19 September 324 and 22 May 337, Constantine the Great was emperor of the whole Roman empire (West and East). After 1 March 317, his son Constantine II was Caesar (junior ruler) under him. After 13 November 324, his son Constantius II was also Caesar (junior ruler) under him.