The first 300 years of Christianity were marked by the existence of several communities that articulated their faith in different ways; Until Constantine, there was no central authority to determine dogmas and rituals. In the 2nd century, the writings of the Church Fathers produced what eventually became Christian dogma. Many of the same ideas are evident in Constantine`s letters and speeches. The same Church Fathers had invented the concept of orthodoxy (correct faith) against other views considered heresy. Under Constantine, heresy was defined according to these earlier Christian views. The property of the heretics was confiscated and their execution was carried out at the stake. The Church Fathers had noted that only the gospels of Mark, Matthew, Luke and John contained correct teaching against the Gnostic gospels, and many scholars believe that these four, found in the later Codex Sinaiticus (an early version of the Bible in the 4th century AD), became official under Constantine. The reverse of this coin depicts the pagan goddess Sieg, walking to the left, carrying a trophy and dragging a prisoner, with the inscription SALVIS REIPVBLICAE, which means “salvation of the Republic”. There is also something that seems to be a christogram in the middle of the composition, just to the left of Victory. While Theodosius is often portrayed in history as the empire freed from the traces of paganism, this piece raises an important juxtaposition concerning the continuation of images of victory in early Christian art, until it is finally replaced by images of angels (Dubois 2016). We desire that all the different nations, subject to our gentleness and moderation, continue to profess this religion transmitted to the Romans by the divine apostle Peter. and which is now manifested by Pope Damasus and Peter, Bishop of Alexandria.
During Constantine`s lifetime, Praxagoras of Athens and Libanius, pagan authors, showered Constantine with praise and portrayed him as a model of virtue. However, his nephew and son-in-law Julian the Apostate wrote the Symposium of Satire or Saturnalia in 361, after the death of the last of his sons; she denigrated Constantine, called him inferior to the great pagan emperors, and indulged in luxury and greed.  According to Julian, Eunapius began—and Zosimus continued—a historiographical tradition that accused Constantine of weakening the empire by his clemency toward Christians.  During his tenure, Constantine adopted reforms aimed at strengthening his regime. One of these reforms was a reorganization of the army, which helped Constantine when he confronted tribes such as the Visigoths and Sarmatians. According to Eusebius, Constantine had commissioned him in 331 to provide fifty volumes of writings for the churches of Constantinople, bound in leather and easily transportable.  It is only known that three or four churches existed during the reign of Constantine, but others seem to have been planned or founded for which the writings were commissioned.  The volumes were probably gospels containing the canonical gospels of the four evangelists rather than complete Bibles containing the entire biblical canon, which were very rare in antiquity.  Constantine chose the practice followed by the churches of Rome: the first Sunday after the first full moon after the spring solstice. Later legal texts under Theodosius I (r. 379-395 AD) and Justinian I (r.
527-565 AD) claimed that Constantine had also created laws against Jews: Jews were not allowed to seek converts, it was forbidden to own Christian slaves, and could not circumcise their slaves. Christians who converted to Judaism were to receive the death penalty. On the other hand, the Jewish clergy were offered the same tax exemptions as Christians. The most important turning point for Christianity in the Roman Empire came in the form of a vision for the future to unify Constantine, nearly three hundred years after Jesus` death. According to Constantine`s chosen biographer, who was a bishop, Jesus Christ gave him the image of a sacred sign that protected him from his enemies, including his adversaries, whom he would soon defeat, and allowed him to reunify the Roman Empire. According to this view, Constantine legalized Christianity and promoted religious tolerance in 313 AD through the Edict of Milan. Maximian`s death necessitated a change in Constantine`s public image. He could no longer rely on his ties to the former Emperor Maximian and needed a new source of legitimacy.  In a speech in Gaul on July 25, 310, the anonymous orator revealed a previously unknown dynastic connection to Claudius II, a 3rd century emperor known for defeating the Goths and restoring order to the empire. The speech breaks with tetrarchic models and emphasizes Constantine`s ancestral prerogative to govern rather than the principles of imperial equality. The new ideology expressed in the speech made Galerius and Maximian irrelevant to Constantine`s right to rule.  Indeed, the speaker emphasizes descent to the exclusion of all other factors: “No accidental coincidence of men or unexpected consequence of favor has made you emperor,” explains the orator Constantine.
 Constantine`s second involvement in an ecclesiastical question followed the defeat of Licinius, but the controversy over Arianism, with its complex explorations of the exact nature of the Trinity formulated in difficult Greek, was as far removed from Constantine`s formation as from his impatient and urgent disposition. The Council of Nicaea, which opened in early summer 325 with a speech by the emperor, had already been preceded by a letter to the main protagonist, Arius of Alexandria, in which Constantine expressed his opinion that the dispute was encouraged only by excessive leisure and academic conflicts, that the point of contention was trivial and could be resolved without difficulty. His optimism was not justified: neither this letter, nor the Council of Nicaea itself, nor the second letter in which Constantine insisted that his conclusions be adopted, were sufficient to resolve a dispute in which the participants were as intransigent as the subtle theological questions. In fact, for more than 40 years after Constantine`s death, Arianism was in fact the official orthodoxy of the Eastern Empire. Constantine became Western Roman Emperor. He soon used his power to address the status of Christians and issued the Edict of Milan in 313. This proclamation legalized Christianity and allowed freedom of worship throughout the empire. Constantine took sole control of the empire in 324 AD. Rome, however, has lost its luster for him. Tensions between the pagans of the city and the Christian emperor remained high. Moreover, from a military point of view, Constantine realized that it would be easier to repel threats from the east and protect valuable territories—and granaries—in Egypt if he moved his capital to a more defensible location in the east. He left Rome forever to build an imperial city that would glorify both his power and his faith.
Constantine`s laws applied and reflected his Christian attitudes. Crucifixion was abolished for reasons of Christian piety, but replaced by hanging to demonstrate the preservation of Roman supremacy. On March 7, 321, Sunday, which was sacred to Christians as the day of the resurrection of Christ and the Roman sun god Sol Invictus, was declared an official day of rest. On that day, markets were banned and public offices closed, except for the purpose of freeing slaves.  However, there were no restrictions on the performance of agricultural work, which was the work of the vast majority of the population, on Sundays.  Latin-rite Catholics considered it inappropriate that Constantine was baptized on his deathbed only by an unorthodox bishop, and in the early 4th century a legend emerged that on the eve of Pope Silver I had cured the pagan emperor of leprosy. According to this legend, Constantine was baptized and began to build a church in the Lateran Basilica.   Constantine`s donation appeared in the 8th century, probably during the pontificate of Pope Stephen II, in which the newly converted Constantine handed over “the city of Rome and all the provinces, districts and cities of Italy and the western regions” to New Year`s Eve and his successors.  In the High Middle Ages, this document was used and accepted as the basis of the pope`s temporal power, although it was denounced as a forgery by Emperor Otto III and denounced by Dante Alighieri as the root of papal worldliness.  The philologist and Catholic priest Lorenzo Valla proved in 1440 that it was indeed a forgery.  During the reign of Emperor Aurelian (r. 270-275 AD), the cult of Sol Invictus (“the invincible and unconquered sun”) was promoted as his family cult.
This cult also embodied the concepts of Jupiter, Apollo and Helios. Sol Invictus merged with another popular military cult, that of Mithras. At the same time, Aurelian also reorganized imperial finances and regulated imports and food prices in the provinces.