The Arch of Constantine - Emperor Constantine Himself

Constantine, also referred to as Constantine the Great, was the son of the emperor Constantius. When his father died in 306 AD, Constantine gained control of the Roman Empire in present-day France and Spain. From this point of power, he then slowly took control of the rest of the Roman Empire, eventually unifying it under his name.

 Constantine is very often credited with converting the Roman Empire to Christianity. His association with Christianity began with a battle for control of the western Roman Empire against Maxentius. Before this battle, Constantine is said to have had a vision from God, showing him a sign from heaven, that said "Conquer in this sign". This battle was an important part of Constantine's move toward sole power of the Mediterranean Basin, and his possession of Rome gave him an edge as an emperor; because he held the old capital, he could claim supremacy over other powerful leaders.

Giulio Romano's "The Battle of the Milvian Bridge"

The next year, in 313 AD, Emperor Constantine signed the Edict of Milan, ensuring religious tolerance for Christians. Christians had been sporadically persecuted during a period referred to as "The Age of Martyrs", a period that had begun after Jesus' death. Some rulers were much harsher than others, but because stories have been exaggerated and fabricated over time it is difficult to tell which persecutions actually occurred historically. There are stories of emperor Nero (64 AD) rounding up Christians by the hundreds and having them brutally executed; burned alive, torn apart by dogs, or in one case even boiled alive publicly. Under emperor Diocletian occurs "The Great Persecution", which was likely on a much smaller scale than is often depicted today. The Edict of Milan also ensured the return of anything confiscated during the times of Christian persecution, and gave them the right to organize and build churches in the Roman Empire.

Accounts depict stories of Christian persecution in the Colosseum, including their being fed to wild animals. 

In the years 313 to 324, Constantine ruled alongside Licinius - dividing the Roman Empire into east and west - but as was commonly true this "partnership" did not last long. There are numerous stories that describe the issues that may have lead up to Constantine's invasion in 323, including a revolt against Constantine and further persecution of Christians by Licinius. Regardless of the catalyst, following Constantine's invasion of Licinius' territory, Licinius declared war on Constantine and the two fought until Licinius' retreat.

Following his victory over Licinius, Constantine unified the Roman Empire in 324 AD. The emperor built his power in Byzantium, which was renamed Constantinople and was referred to as the "second Rome". This dedication of the new capital confirmed the divide between the emperors and Rome. The capital became wherever the emperor was and Rome, though still prestigious and historically significant, lost nearly all of its political significance.

Constantine moved the capital to Istanbul, in large part, because that part of the world was much more developed and economically sound that the newer region of Italy. 

Constantine took part in the first meeting of the Christian churches at the Council of Nicea in 325 AD. This council was called together in an effort to fin common ground in the churches' doctrines and traditions of practice. The quest for a unified Christianity was not fulfilled during the first few sessions, because the council was stuck as to whether Christ was lesser to God or equal to him. Eventually a set of rules, deemed the Nicean Creed, was defined.

Constantine considered himself and Christian and to have a personal relationship with the Christian God, however there is some speculation that his conversion to Christianity did not actually occur until much later in his life. Some sources say that Constantine did not fully understand the Christian doctrines and their implications after his conversion, and this could be a reason for his actions not always aligning with the Christian faith. He continued to encourage the Roman people, to a degree, to worship him, which is considered idolatry in the Christian faith and breaks the number one foundation of Christianity ("You shall have no other God before me"). Some people infer that Constantine used Christianity as a political tool, and did not actually convert until his baptism on his death bed in 337 AD.

Remaining pieces of a large marble statue of Constantine - now located in the Capitoline Museum - circa 312 AD.