Constantine (I) the Great (280?–337 A.D.), Roman emperor from 308 to 337. Constantine's reign was marked by two major events—a tremendous growth of Christianity and the moving of the capital of the empire from Rome to Constantinople.
Constantine was born in Illyricum, a Roman province on the Balkan peninsula. His mother, Helena, was the daughter of an innkeeper. His father, Constantius (sometimes called Constantius Chlorus), became an Augustus, or coemperor, responsible for the western part of the empire, upon the retirement in 305 of the coemperors Diocletian and Maximian. When Constantius died in 306, Constantine succeeded in having himself named Caesar, or imperial heir, to Maximian, who resumed the coemperorship.
A struggle for power soon developed, and in 308 Constantine was elevated to Augustus, an honor he shared with five co-emperors. He caused Maximian to be killed in 310 and defeated Maximian's son Maxentius, the emperor in Italy, at the Battle of Milvian Bridge outside Rome in 312. By this victory, Constantine became undisputed emperor in the West. The triumphal Arch of Constantine was built in Rome in 315 to commemorate the battle.
In the East, one Augustus died in 311, and in 313 Licinius defeated the remaining rival to become emperor of his region. Constantine campaigned against Licinius in 314, but they came to an agreement that gave the empire a decade of internal peace. In 324 Constantine overthrew Licinius and united the empire under his own rule.
Constantine's conversion to Christianity began in 312. Before the Battle of Milvian Bridge, Constantine reportedly saw or dreamed of a flaming cross and the words In hoc signo vinces ("In this sign you will conquer"). After his victory, he took a Christian symbol as his standard. A year later, in the Edict of Milan, he proclaimed religious toleration for Christians.
Contantine sought to maintain a unified Christian church in support of his rule. He called together important churchmen at the Council of Nicaea (325) in hope of ending the Arian controversy. Out of this meeting came the Nicene Creed, a statement of faith that defined clearly the doctrine of the Trinity. With the approval of the emperor, Christianity spread rapidly; in gratitude, Christians called Constantine "the Great." He exempted the clergy and church property from taxes. Constantine was baptized on his deathbed.
Rome was no longer the strategic center of the empire. In 330 Constantine moved to his new capital city of Constantinople (City of Constantine), which he had built on the site of Byzantium on the strait of Bosporus, according to instructions received in another dream. Christianity was the official religion of Constantinople.
Since many Romans had evaded oppressive taxes by leaving their communities, Constantine decreed that the economic classes of craftsmen and tenant farmers were to be hereditary. The class of landowners had already been made hereditary by the emperor Diocletian (284–305). This class system continued for hundreds of years and provided a basis for feudal society.
Before his death, Constantine partitioned the empire among five heirs. This act destroyed the unity he had achieved with such effort and led in time to a permanent division between East and West.