Constantine the Great
Gaius Flavius Valerius Aurelius Constantinus, better known as Constantine I, emperor of Rome from A.D. 306 until his death in A.D. 337, is called the most important Roman emperor in late antiquity. He was born on February 27, in the early 270s, in what is now Serbia, but was then the Roman province of Moesia. His father was to become Emperor Constantius I, but was a military officer at the time of Constantine's birth. His mother was Helena, who became a saint in the Roman Catholic and Eastern Orthodox Church. Constantine completed the major necessary administrative reorganization of the Roman emperor that had been begun by Emperor Diocletian (ruled 284-305), waged successful wars against barbarians -- the Franks, Alamanni, Visigoths, and Sarmatians -- on the borders of the Empire, moved the capital of the Roman Empire to Byzantium, and legalized Christianity.
While Constantine was a teen, Emperor Diocletian began the reorganization of the Roman Empire into what is known as the "tetrarchy," a word which comes from Greek words for "4" and "rule." The tetrarchy was a division of the Empire into two parts, an eastern and a western, with emperors (called "Augustus") in charge of each. Under each Augustus was a lesser emperor referred to as "Caesar" who, while being groomed for the higher office, could act in his own right as the head of an army. The eastern and western parts of the Empire were subdivided to allot provinces to the Caesars. Diocletian appointed Maximian as the Augustus for the western section of the Empire, and Maximian chose Constantine's father, Constantius, as his Caesar. Diocletian, who kept command of the eastern section (which came to be known as "Byzantine"), chose as his Caesar a man named Caius Galerius Valerius Maximianus, better known as Galerius.
It seems odd that an emperor would deliberately give up half of his land to another, as Diocletian did in 285. However, the administration of a gigantic empire that spread to Persia in the East, Britain in the West, the Rhine and Danube in the North, and the northern area of Africa to the south proved impossible for Diocletian alone, especially since there were regular attacks and rebellions along the northern border and conflict in the East.
Diocletian's reforms in the 290s included renewal of the imperial cult. Roman citizens were compelled to worship those dead emperors who had been named gods by act of the senate. They also had to revere the "genius" or spirit that was protecting the living emperors and prostrate themselves before the purple-clad rulers. Diocletian believed such worship was necessary for the security of the Empire. This is a typically Roman way of thinking. During the Roman Republic, the Vestal Virgins had been treated with great respect because they were believed to hold the luck of Rome. Christians, who refused to worship the emperors, were persecuted. Although Christians had been persecuted on and off since the Crucifixion, the 8-year persecution of Diocletian is known as the Great Persecution.
Diocletian did not just give up half the empire. In 305 he and his co-Augustus, Maximian, abdicated. Constantius and Galerius became the new Augusti (the plural of Augustus). New Caesars were needed. Reverting to the emperor-selection processes from before the tetrarchy, the imperial army in Britain acclaimed Constantine emperor on July 25, when his father, Constantius I, died in York, in 306; those in Rome chose Maximian's son, Maxentius. Of the two, Galerius, the eastern Augustus, accepted Constantine as Caesar of the west. Galerius made his nephew Caius Valerius Galerius Maximinus (known as Maximinus or Maximinus Daia) Caesar in the east. There was no western Augustus, so Galerius appointed Flavius Valerius Severus, and when Severus died, Valerius Licinianus Licinius. Before his death in 311, Galerius promoted Constantine and Maximinus to Augusti. That made four legally appointed Augusti (Galerius, Constantine, Maximinus, and Licinius), plus Maxentius, who also claimed the title of Augustus.
Licinius held what we call Eastern Europe, the Roman provinces of Illyricum (modern Albania), Thrace and Pannonia (modern Austria, Croatia, Hungary, Serbia, Slovenia, Slovakia, and Bosnia and Herzegovina). Constantine was in charge of Britain, Gaul, the Roman province of Germany, and Spain, with his army stationed at the Rhine frontier, the source of many barbarian threats.
In 312, a year before Constantine established a stronghold on the dangerous and troublesome right-hand side of the Rhine and Danube -- the area from which the Goths under Alaric would later descend upon Rome, Constantine defeated Maxentius (who still held Italy), at the Milvian Bridge, near Rome. This was an important battle for the history of Christianity because Constantine claimed the night before the battle he had a vision telling him we would win if he fought under the sign of Christ. Constantine did as the vision directed. Although Constantine did not officially become a Christian until his deathbed baptism, he called himself one (the first Roman emperor to do so) and interfered with Church policy from this point on.
In 313, in which year Licinius defeated the eastern Augustus, Maximinus, Constantine met with Licinius in Milan, Constantine's sister married Licinius, and the two Augusti -- Constantine and Licinius -- issued what is called the Edict of Milan, a bill granting religious freedom to Christians. This was not the first edict of tolerance, but it put Christianity on the same playing field as paganism. Licinius went along with the edict, although he did not support the new religion.
By 316 the two Augusti were at each other's throats. Although the battles between the two men were not decisively in Constantine's favor (Constantine won the first and the second was a draw), a settlement made in 317 granted Constantine all European provinces of the Roman Empire except Thrace. Hostilities erupted again seven years later. This time Constantine decisively defeated Licinius, beating him at Adrianople, in Thrace, and on the Bosporus. Despite his sister's pleas for her husband, Constantine executed Licinius.
By 325 the tetrarchy was a memory. As sole Augustus, Constantine hosted the first Ecumenical Council of the Christian Church. It was called the Council of Nicea and it set Church policy on the relationship between two of the three components of the Christian trinity, leaving the Holy Spirit for later discussions. Today's Nicene Creed came out of that Council.
In A.D. 330, Constantine moved his capital to Byzantium, which he re-named Nova Roma 'New Rome' and provided with the necessities of a Roman Imperial capital city, including a senate and civic offices. Byzantium was a rich city situated between Europe and Asia, with access to the Balkans and the Mediterranean Sea. Constantine increased Byzantium's size four-fold, built new walls, and started two churches, the Hagia Sophia 'Holy Wisdom' and the Hagia Eirene 'Holy Peace'. Upon Constantine's death in A.D. 337, Nova Roma was named Constantinople, and Constantine, the first Christian emperor, was deified, like many of his pagan predecessors. 'Constantine's City' remained the center of the Byzantine Empire until its fall in 1453. It was only in the Twentieth Century that Constantinople became Istanbul.
While Constantine made great strides towards overcoming the barbarian threat along the northern frontier and would have tried his hand at Persia if he had lived, he is known not so much for his military prowess as for moving the capital of the Roman Empire to an exciting, viable, wealthy new location, and for his legitimizing Christianity. During his reign, he not only killed his brother-in-law, but his own wife and son. Despite his ruthlessness, Constantine was made into a saint. Historians labeled him Constantine the Great.