Figure 1: Emperor Constantine I is often credited with converting the Roman Empire to Christianity. nationalgeographic
Figure 2: Emperor Constantine I, presenting a model of the city to the Blessed Virgin Mary. Detail of the southwestern entrance mosaic in Hagia Sophia.
Augustus (from 25 July 306); born Naissos 273/4, died Nikomedeia 22 May 337; feastday 21 May. Son of Constantius Chlorus and Helena, he was proclaimed as augustus in Britain upon the death of his father. He was subsequently acknowledged as caesar by Galerius and as augustus by Maximian, and his imperial position was confirmed at the Conference of Carnuntum in 308. He defeated Maxentius at the battle of the Milvian Bridge in 312, thus becoming sole ruler of the West. Alliance with Licinius turned to hostility, and after victory over his rival at Chrysoupolis in Bithynia in 324 Constantine became ruler of the whole empire. He associated his sons with him as caesars—Crispus (317), Constantine II (317), Constantius II (324), and Constans I (333)—but he remained sole augustus until his death. He had two consorts, Minervina (perhaps a concubine) and Fausta (see genealogical table).
Constantine carried out important administrative and military reforms, completing and/or reversing those of Diocletian. He organized the entire empire into three or four prefectures, each under its own praetorian prefect, below whom were provinces and the cities. At court, officials such as the comes rei privatae, comes sacrarum largitionum, and magister officiorum, wielded great power as heads of large amorphous bureaus, while magistri militum commanded the army, increasingly dominated by the comitatenses. Constantine reformed the coinage, issuing a gold solidus that remained the standard coin through the 11th C. To celebrate his victory over Licinius he founded a new city on the site of ancient Byz.; Constantinople was inaugurated on 11 May 330, not so much a “new capital” as an imperial residence and monument to the emperor's greatness. According to the Chronicon Paschale (1:527–29), his huge building program consisted almost entirely of secular structures, whereas Eusebios of Caesarea emphasizes the churches and martyria that Constantine built in the capital and at Nikomedeia, Antioch, and Jerusalem.
Like most of his predecessors, Constantine sought divine support for his rule and ultimately came to base his power on a special connection with the Christian God. This concept developed slowly, augmented by the emperor's victories, and culminating in the image of Constantine in the works of Eusebios of Caesarea, esp. the Vita Constantini. In the latter work (VC 4.15) Eusebios interprets the upward gaze exhibited by Constantine on his coins as a gesture of piety. In fact, his numismatic portraits exhibit a remarkable range of types (D.H. Wright, DOP 41  493–507). It is still debated whether Constantine actually issued the so-called Edict of Milan. Constantine became involved in the controversies surrounding Donatism and Arianism, convoked the first ecumenical council at Nicaea, and approved its decisions, although he later came to support Arianism. He was baptized on his deathbed by Eusebios of Nikomedeia. The so-called Donation of Constantine is a forgery, probably of the 8th C.
As the first Christian emperor and the founder of Constantinople, Constantine set the style that was followed by nearly all Byz. emperors. Despite his very real human failings, Constantine was very quickly heroized as founder of the new politico-religious order and regarded as a saint; he was commonly pictured, frequently along with his mother, in figural representations of rulers in church decoration.Timothy E. Gregory, Anthony Cutler
Kazhdan, Alexander, ed. The Oxford Dictionary of Byzantium. New York: Oxford University Press, 1991.oxfordreference