Constantine the Great was the first Roman ruler to be converted to Christianity. He was the founder of Constantinople, which remained the capital of the Eastern Roman Empire until 1453.
Constantine the Great was born Flavius Valerius Constantinus in what is now Serbia. He was the son of the commander Constantius Chlorus and Helena. Constantius became co-emperor in 305. Constantine, who had shown military talent in the East, joined his father in Britain in 306. He was popular with the troops, who made him emperor when Constantius died later the same year. Over the next 20 years Constantine had to fight his rivals for the seat as emperor, and he did not finally consider himself as a complete ruler until 324.
Constantine always tried to follow in the footsteps of his father and earlier 3rd-century emperors. In 312, on the day before a battle against Maxentius, his rival in Italy, Constantine is said to have dreamed that Christ appeared to him and told him to write the first two letters of his name (XP in Greek) on the shields of his troops.
The next day he is said to have seen a cross on the sun and the words "in this sign you will be the victor." Constantine then defeated Maxentius at the Battle of the Milvian Bridge, near Rome. The Senate named the winner as the savior of the Roman people. Due to this Constantine now looked upon the Christian god as a bringer of victory. Persecution of the Christians was ended, and Constantine's co-emperor, Licinius, joined him in issuing the Edict of Milan (313), which allowed people to follow the Christian religion in the Roman Empire. Because Christianity was Constantine's favored religion, the Christian church was then given legal rights and large donations.
A struggle for power soon...