This took place in 312 at the Battle of Eagle Bridge where Constantine defeated Maxentius. Historian Eusebius of Caesarea (biographer of St. Constantine) and apologist Lactantius describes the vision that St. Constantine had before battle. Thus, he saw the sky, day, bright cross above the sun, with the inscription “in hoc signo vinces” (in this sign you will conquer). At night, in a dream and Savior appeared, asking him to put on his army flags Holy Cross as a sign that was protective in the fight. This flag the brand name Christian was called labarum. The event is called, by many researchers, converting the king to Christianity.
In January 313, Emperor Constantine gave an act by which Christianity became “religious tender,” ie religion allowed, like other religions in the empire. Furthermore, certain religious and moral value of Christian doctrine, recommended to everyone. But Constantine did not declare Christianity the state religion, as sometimes erroneously stated. This step was taken in the year 380, the Emperor Theodosius the Great.
In 325, Saint Constantine convened the First Ecumenical Council in Nicaea place (in Turkey). With the priority preservation of the unity of the Roman Empire, the king summoned all the bishops of the Church to decide the issue of the heresy of Arius. They claim that Jesus Christ is the Son of God, but is the first creature of the Father. At this meeting attended, according to tradition, 318 fathers, including St. Athanasius the Great, St. Nicholas of Myra, St. Spyridon of Tremithus, St. Paphnutius of Egypt and Osiu of Cordoba. Following the work, the council established the divinity of the Son, while composing the first seven articles of the Creed, set the date of Easter (the first Sunday after the full moon after the vernal equinox) and gave 20 canons on ecclesiastical discipline. At the end of the work, when the Cordoba Osiu spoke for the first time Creed, Constantine said, “Yes, this is true.’m Not a theologian, but I feel that this is the truth.’m Sure you will not do, but God worked with you. “
At the same time, Constantine built a impressive fortress on the left bank of the Bosphorus, the site of the ancient city Byzantion. City that will bear his name (Constantinople) will be the new capital of the empire, to rival ancient Rome. Here he built the great cathedral dedicated to the Holy Apostles, where he was buried.