During the persecution of Christians under Diocletian (302-306 AD), the emperor had ordered not only arrests, but also the Christian clergy to hand over their sacred texts. In order to avoid detention and arenas, some, including bishops, had done so. Divisions between Christian communities had increased, and one group, led by Bishop Donatus, insisted that these bishops were now polluted. The bishops asked Constantine to mediate in this matter. After so many civil wars, Constantine was determined to promote unity throughout the Roman Empire and ordered a policy of «forgive and forget.» Despite the skeptics, there is no doubt that the union of Church and State of Constantine contributed to the growth of Christianity and the development of its theology. Constantinople became the seat of the Byzantine Empire, which ruled the entire Middle East until the conquest of Islam in 1453: the fall of Constantinople. In 325 AD, Constantine`s mother, Helena, made a pilgrimage to Israel. There, she claimed to have discovered the places related to Jesus, including the «true cross.» Constantine then built the Church of the Nativity in Bethlehem and the Church of the Holy Sepulchre (where Jesus` tomb is located) in Jerusalem. The first documented official persecution of Christians on behalf of the Roman Empire took place in 64 AD, when, as reported by Roman historian Tacitus, Emperor Nero attempted to blame Christians for the great fire of Rome. According to church tradition, Peter and Paul were martyred during Nero`s reign in Rome.
Modern historians, however, debate whether the Roman government distinguished between Christians and Jews before Nerva changed the Fiscus Judaicus in 96, whose observant Jews paid the tax and Christians did not. Constantine ruled the Roman Empire as sole emperor for much of his reign. Some scholars claim that its main purpose was to obtain unanimous consent and submission to its authority from all classes, and therefore chose Christianity to carry out its political propaganda, believing that it was the most appropriate religion that could suit imperial worship (see also Sol Invictus). Regardless, Christianity spread throughout the empire under the Constantinian dynasty, ushering in the era of the state church of the Roman Empire.  Whether Constantine sincerely converted to Christianity or remained faithful to paganism is controversial among historians (see also Constantine`s religious policy).  His formal conversion in 312 is almost universally recognized among historians, although it has been claimed that he was baptized only on his deathbed by the Arian bishop Eusebius of Nicomedia in 337;    The real reasons for this remain unknown and are also discussed.   According to Hans Pohlsander, professor emeritus of history at the University at Albany, SUNY, Constantine`s conversion was just another instrument of realpolitik in his hands to serve his political interest in keeping the empire under his control: a large gold-covered pole had a crossbar that formed the shape of a cross. At the top, a crown of precious stones and gold had been attached. On it, two letters, imitating the name «Christ» by their first letters, formed the monogram of the title of the Savior, with Rho interspersed with chi in the middle. On the crossbar, which was cut in half from the post, hung a cloth.
But the vertical post. bore the golden portrait of the head and shoulder of the beloved emperor and his sons. Constantine I (Latin: Flavius Valerius Constantinus; Greek: Κωνσταντῖνος Konstantinos; Constantine the Great (27 February 272 † 22 May 337) was Roman Emperor from 306 to 337 and the first to convert to Christianity. He was the son of Flavius Constantius, a Roman officer of Illyrian origin who had been one of the four rulers of the tetrarchy. His mother, Helen, was Greek and Christian and of low birth.     Constantine served with distinction under the Roman emperors Diocletian and Galerius. He began his career campaigning in the eastern provinces (against the barbarians and Persians) before being recalled to the west in 305 AD to fight alongside his father in Britain. After his father`s death in 306, Constantine became emperor. He was celebrated by his army at Eboracum (York, England) and eventually emerged victorious from the civil wars against the emperors Maxentius and Licinius to become the sole ruler of the Roman Empire in 324.
the Christ of God appeared to him with the sign that had appeared in heaven, exhorting him to make a copy of the sign that had appeared in heaven and use it as protection against the attacks of the enemy. The Holy Roman Empire counted Constantine among the venerable figures of its tradition. In the later Byzantine state, it became a great honor for an emperor to be celebrated as the «new Constantine»; ten emperors bore this name, including the last emperor of the Eastern Roman Empire.  Charlemagne used monumental Constantinian forms at his court to suggest that he was Constantine`s successor and equal. Constantine acquired a mythical role as a warrior against the pagans. His reception as a saint seems to have spread throughout the Byzantine Empire during the wars against the Persians and Sassanid Muslims in the late 6th and 7th centuries.  The motif of the Romanesque horseman, the figure mounted in the posture of a triumphant Roman emperor, became a visual metaphor in statues praising local benefactors. The name «Constantine» experienced a resurgence in popularity in western France in the 111th and 12th centuries.
 Constantine`s monetary policy was closely linked to his religious policy; The increase in minting was associated with the confiscation of all gold, silver, and bronze statues from pagan temples between 331 and 336, which were declared imperial property. Two imperial commissioners for each province were responsible for procuring the statues and melting them down for immediate minting, with the exception of a number of bronze statues used as public monuments in Constantinople.  Ambrose, the bishop of Milan, who was a spiritual and political adviser to Theodosius, was furious. He refused to give communion to Theodosius until the emperor publicly repented: he had to set aside his royal robes, put on a shroud, and publicly ask for God`s mercy. The Battle of the Milvian Bridge outside Rome in 312 AD was a turning point for Constantine. He defeated a rival, his brother-in-law Maxentius, and won the mantle of the Western Roman emperor. But a revelation he experienced before the battle was far more important. Constantine appeared in the midst of the so-called Great Persecution, which began in 303 under Emperor Diocletian.
In 305, the problems caused by the persecution were overtaken by those who determined Diocletian`s successor. More than six different generals fought to become the next emperor. Constantine distinguished himself by becoming a Christian and shamelessly making Jesus the patron saint of his army. By 313, only two competitors remained, Constantine and Licinius. The two jointly issued the Edict of Milan, which made Christianity a legal religion and officially ended the persecution. But it was not until 324 that Constantine finally became the sole ruler of the Roman Empire. In the cultural realm, Constantine revived the closely shaved facial fashion of previous emperors, originally introduced by Scipio Africanus to the Romans and transformed by Hadrian into bearding. This new Roman imperial fashion lasted until the reign of Phocas in the 7th century.   In 321 he decreed that Venerable Sunday should be a day of rest for all citizens.  In 323 he issued a decree forbidding Christians to participate in state sacrifices.  After the pagan gods had disappeared from his coins, Christian symbols appeared as attributes of Constantine, the Chi Rho in his hands or on his labarum, as well as on the coin.  The reign of Constantine set a precedent for the emperor, who had great influence and authority in early Christian councils, especially in the dispute over Arianism.
Constantine did not like the risks to social stability posed by religious conflicts and controversies and preferred to establish an orthodoxy.  His influence on the councils of the Church was to apply doctrine, eradicate heresy, and maintain ecclesiastical unity; The role of the church was to determine correct worship, doctrines, and dogmas.  Constantine I`s father became Western Roman Emperor in 305. After his father`s death, Constantine fought for power. He became emperor of the West in 312 and sole Roman emperor in 324. Constantine was also the first emperor to join Christianity. He issued an edict protecting the Christians of the empire and converted to Christianity on his deathbed in 337. According to Constantine`s biographer, Eusebius, Constantine and his troops saw a cross of light in the sky, as well as the Greek words for «to win in this sign.» That night, Constantine had a dream in which Christ confirmed the message. The emperor marked the Christian symbol of the cross on the shields of his soldiers.
When he triumphed at the Milvian Bridge, he attributed the victory to the God of the Christians. Modern scholars still debate history and whether Constantine`s conversion was sincere or a political maneuver. Separately, Constantine met Licinius, the Eastern Emperor, in 313 AD, and together they issued the Edict of Milan.