Constantine I, aka Constantine the Great, was Roman emperor from 306 to 337.
He served with distinction under the Roman emperors Diocletian and Galerius.
He made Christianity the main religion of Rome and created Constantinople, his chosen eastern capital city — which became the most powerful city in the world.
His reign is said to be the demarcation between ancient history and the Middle Ages.
It is recorded that on the evening of October 27 as his armies preparing for the upcoming battle in the year 312 Constantine is said to have received his famous Vision of the Cross.
This appeared as a cross of light in the heavens above the sun which bore inscription In Hoc Signo Vinces which means "In this sign thou shalt conquer".
It is further recorded that this vision led him to fight under the protection of the Christian God.