On the death of his father Constantius I in 306 at Eboracum (York) the army proclaimed him emperor. After a period of political complications, with several emperors competing for power, Constantine and Licinius divided the empire between them, East and West. War was fought between the two rulers (314) and Constantine defeated and killed Licinius (323) and he became sole emperor, founding a new second capital at Byzantium, which he named Constantinople (now Istanbul).

He adopted Christian symbols for his battle standards in 312 prompted by a “vision” of the sign of the cross in the rays of the sun. In the following year he proclaimed tolerance and recognition of Christianity in the “Edict” of Milan. Although his own beliefs are uncertain he supported orthodox Christianity in an attempt to maintain the unity of the vast Roman empire. Sunday was declared a holiday in 326. He and his mother Helena took great interest in the Christian sites of Rome and Palestine. Basilicas were built on the site of the stable-cave in Bethlehem, where Jesus Christ was supposed to have been born, his alleged tomb in Jerusalem, and St Peter’s grave on the Vatican hill in Rome, and at Constantinople (St Sophia). The Eastern Church lists him as a saint.