Flavius Valerius Aurelius Constantinus

Flavius Valerius Aurelius Constantinus was born in Naissus (modern Niš, Serbia) in the province of Moesia Superior on 27 February ca. 280 to Roman general and later Western Roman Emperor Constantius Chlorus, and his first wife St. Helena. Helena, who played a very influential role throughout her son's life, was of modest background; Ambrose writes that she worked in an inn. His father left his mother around 292 to marry Flavia Maximiana Theodora, daughter (or step-daughter) of the Western Roman Emperor Maximian, although Constantine fully reinstated his mother, St. Helena, as "Augusta, mother of Caesar" after his father's death. Theodora would give birth to six half-siblings of Constantine, including Julius Constantius.

Young Constantine received a formidable education, became a fluent speaker of Greek, and was adept in philosophy. He served at the court of Diocletian in Nicomedia, after the appointment of his father as one of the two caesares (junior emperors) of the Tetrarchy in 293. In 305, both augusti (senior emperors), Diocletian and Maximian, abdicated, and Constantius succeeded to Maximian's position of western augustus. Although two legitimate sons of emperors were available (Constantine and Maxentius, the son of Maximian), both of them were ignored in the transition of power. Instead, Severus and Maximinus Daia were made caesares. Constantine subsequently left Nicomedia to join his father in the Roman Gaul; however, Constantius fell sick during an expedition against the Picts of Caledonia, and died on July 25, 306 in Eboracum (York). The general Chrocus, of Alamannic descent, and the troops loyal to Constantius' memory immediately proclaimed Constantine an augustus. Under the Tetrarchy, Constantine's succession was of dubious legitimacy. While Constantius as senior emperor could "create" a new caesar, Constantine's (or, his troops') claim to the title of augustus ignored the system of succession established in 305. Accordingly, Constantine asked Galerius, the eastern augustus, to be recognized as heir to his father's throne. Galerius granted him the title of caesar, confirming Constantine's rule over his father's territories, and promoted Severus to augustus of the West.

Constantine is perhaps best known for being the first Christian Roman Emperor. His reign was a turning point for the Christian Church. In 313 Constantine announced toleration of Christianity in the Edict of Milan, which removed penalties for professing Christianity (under which many had been martyred in previous persecutions of Christians) and returned confiscated Church property. Though a similar edict had been issued in 311 by Galerius, then senior emperor of the Tetrarchy, Constantine's lengthy rule, conversion, and patronage of the Church redefined the status of Christianity in the empire.

Scholars debate whether Constantine adopted his mother St. Helena's Christianity in his youth, or whether he adopted it gradually over the course of his life. Constantine was over 40 when he finally declared himself a Christian. Writing to Christians, Constantine made clear that he believed he owed his successes to the protection of the Christian High God alone. Throughout his rule, Constantine supported the Church financially, built various basilicas, granted privileges (e.g. exemption from certain taxes) to clergy, promoted Christians to high ranking offices, and returned property confiscated during the Great Persecution of Diocletian. His most famous building projects include the Church of the Holy Sepulchre and Old Saint Peter's Basilica.

The reign of Constantine established a precedent for the position of the Christian Emperor in the Church; Constantine considered himself responsible to God for the spiritual health of his subjects, and thus he had a duty to maintain orthodoxy. For Constantine, the emperor did not decide doctrine - that was the responsibility of the bishops - rather his role was to enforce doctrine, root out heresy, and uphold ecclesiastical unity. The emperor ensured that God was properly worshipped in his empire; what proper worship consisted of was for the Church to determine.

In 316, Constantine acted as a judge in a North African dispute concerning the heresy of Donatism. More significantly, in 325 he summoned the Council of Nicaea, effectively the first Ecumenical Council (unless the Council of Jerusalem is so classified), to deal mostly with the heresy of Arianism.