Flavius Valerius Constantinus, known as St. Constantine the Great or St. Constantine I, Emperor and Equal-to-the-Apostles (February 27, 272 to May 21, 337) was first Christian Emperor, responsible for spreading the faith all over the Empire. The Orthodox Church keeps his feast on May 21, along with his mother, Empress Saint Helen, as Holy Equals-to-the-Apostles.
St. Constantine the Great and his Mother St. Helen
Constantine is perhaps best known for being the first Roman Emperor to endorse Christianity, traditionally presented as a result of an omen — a chi-rho in the sky, with the inscription "By this sign shalt thou conquer" — before his victory in the Battle of Milvian Bridge in 312, when Constantine is said to have instituted the new standard to be carried into battle, called the labarum.
Christian historians ever since Lactantius have adhered to the view that Constantine "adopted" Christianity as a kind of replacement for the official Roman paganism. Though the document called the "Donation of Constantine" was proved a forgery (though not until the 15th century, when the stories of Constantine's conversion were long-established "facts") it was attributed as documenting the conversion of the Roman Empire to Christianity for centuries. Even Christian skeptics have accepted this formulation, though seeing Constantine's policy as a political rather than spiritual move.
By the end of the 3rd century, Christian communities and their bishops had become a force to contend with, in urban centers especially. Christians were preferred for high government positions; the Church was granted various special privileges; and churches like the Church of the Nativity in Bethlehem and the Church of the Holy Sepulchre in Jerusalem were constructed. Christian bishops took aggressive public stances that were unknown among other cult leaders, even among the Jews. Proselytism had had to be publicly outlawed, simply to maintain public decorum. In the essential legions, however, Christianity was despised as womanish, and the soldiers followed pagan cults of Mithras and Isis. Since the Roman Emperors ruled by "divine right" and stayed in power through the support of the legions, it was important for them to be seen to support a strong state religion. The contumely of the Christians consisted in their public refusal to participate in official rites that no one deeply believed in, but which were an equivalent of an oath of allegiance. Refusal might easily bring upon all the Roman people the loss of the gods' support; such were the usual justifications for occasional lynchings of Christians by Roman soldiers, the fare of many martyrologies.
Constantine and Licinius' Edict of Milan (313) neither made paganism illegal nor made Christianity a state-sponsored religion. What it did was legalize Christianity, return confiscated Church property, and establish Sunday as a day of worship. Though the church prospered under Constantine's patronage, it also fell into the first of many public schisms. He called the First Ecumenical Council to settle the problem of Arianism, a dispute about the personhood and Godhood of Jesus Christ. It produced the Nicene Creed, which favored the position of Athanasius, Arius's opponent, and became official doctrine.
In medieval times, Constantine was presented as an ideal ruler, the standard against which any king or emperor could be measured.
From his recent illness, Constantine knew death would soon come. Within the Church of the Holy Apostles, Constantine had secretly prepared a final resting-place for himself. It came sooner than he had expected. Soon after the Feast of Pascha in 337, Constantine fell seriously ill. He left Constantinople for the hot baths near his mother's city of Helenopolis (Altınova), on the southern shores of the Gulf of Nicomedia (present-day Gulf of İzmit). There, in a church his mother built in honor of Lucian the Martyr, he prayed, and there he realized that he was dying. Seeking purification, he became a catechumen and attempted a return to Constantinople, making it only as far as a suburb of Nicomedia. He summoned the bishops and told them of his hope to be baptized in the River Jordan, where Christ was written to have been baptized. He requested the baptism right away, promising to live a more Christian life should he live through his illness. The bishops, Eusebius records, "performed the sacred ceremonies according to custom". He chose the Arianizing bishop Eusebius of Nicomedia, bishop of the city where he lay dying, as his baptizer. In postponing his baptism, he followed one custom at the time which postponed baptism until after infancy. It has been thought that Constantine put off baptism as long as he did so as to be absolved from as much of his sin as possible. Constantine died soon after at a suburban villa called Achyron, on the last day of the fifty-day festival of Pentecost directly following Pascha on 22 May 337.
The Church of the Holy Apostles was second in size and importance only to the Hagia Sophia among the great churches of the capital Constantinople. When Constantinople fell to the Ottomans in 1453, the Holy Apostles briefly became the seat of the Ecumenical Patriarch of the Eastern Orthodox Church. Three years later the dilapidated edifice was abandoned, and the patriarchate was moved to the Theotokos Pammakaristos Church. In 1461, the church of the Holy Apostles was demolished by the Ottomans to make way for the Fatih Mosque.
To celebrate St. Constantine's feast day, you can read
"The Story of Saint Constantine"
Troparion (Tone 8)
Having seen the figure of the Cross in the heavens, And like Paul not having received his call from men, O Lord, Your apostle among rulers, the Emperor Constantine. Has been set by Your hand as ruler over the Imperial City That he preserved in peace for many years, Through the prayers of the Theotokos, O only lover of mankind.
Kontakion (Tone 3)
Today Constantine and his mother Helen
Reveal the precious Cross,
The weapon of the faithful against their enemies.
For our sakes, it has been shown to be a great sign, and fearsome in battle.