On May 22, 337, a man entered baptismal waters, publicly declaring his faith in Jesus Christ. And while all baptisms are a momentous occasions, this particular one not only changed the life of the one exiting the water, it also inspired a marked change in direction for an entire land, an entire people, and ultimately an entire world.

Because this wasn’t just any man. This man was Flavius Valerius Constantinus, also known as Constantine I or Constantine the Great, the emperor of the Rome, the most powerful man in the most powerful empire of the entire ancient world.

Born on February 27, circa 280, Constantine was born in modern-day Serbia to his namesake father, an officer in the Roman army, and Helena, a woman who may have been either a wife or concubine to his father. Whatever the case, he soon left her to marry the stepdaughter of Maximian, the Western Roman Empire (the Roman Empire was, at this time, split in two, with separate emperors for each half), sending his son to live with Diocletian, the Eastern Roman Emperor, as a show of goodwill. Following Maximian’s abdication in 305, the elder Constantinus became emperor and, upon his father’s death, Constantine himself was declared Western Emperor by its troops and citizens.

Well…most of them.

A group loyal to the former emperor Maximian declared the throne for his son, Maxentius, and a bloody and brutal civil war erupted throughout the west, lasting over five years and resulting in the death of thousands. In 312, Constantine and his forces encountered Mexentius and his men at the Milvian Bridge on the Tiber River in modern-day Italy. It was there, according to Constantine, that he encountered God for the first time.

Constantine claimed that he saw a vision in the sky, a bright cross with the words “By this sign, conquer” inscribed upon its surface. Awed and inspired, he ordered his men to paint crosses on their shields, which he later said he’d been instructed by Christ in a dream to do. In a defining moment, not only for his newfound faith but also for Rome, under this emblem Constantine was successful in battle, soundly defeating Maxentius and his forces. He entered Rome, claiming once and for all his position as Western Roman Empire.

A position, he believed, was ordained to him by God.

Under previous emperors, Christianity was viewed anywhere from a nuisance to a full-blown crime. Back in A.D. 64, the Great Fire of Rome swept through the city, lasting for over nine days and destroying over 2/3 of metropolis before it was finally quenched. The emperor at the time, Nero, blamed the catastrophe on a new religious sect gaining traction in the streets: Christianity.

His declaration, of course, was made more out of pride and fear than actual evidence. The Christians’ claim of Christ’s kingship didn’t sit well with what the emperor believed was his exclusive right to sovereignty. The people could have all the gods they wanted; what they couldn’t have, however, was another king. But in the oppressed, impoverished, and superstitious culture of the time, the Christians made a more than convenient scapegoat.

Persecution lasted for centuries, with some periods being more intense than others. Punishments ranged anywhere from mob violence, assault, public stoning, and robberies, to more government sanctioned oppression such as the decree issued by Decius in 250 requiring a public sacrifice as a way to worship and offer testimony of allegiance to the emperor. Christians, bound by their vow to worship no one but the True God, were arrested, imprisoned, tortured, and often executed for their refusal.

All of that began to change after Constantine. Remembering his vision on the battlefield and what he viewed as divine intervention on his behalf, soon after coming to power, he helped draft the Edict of Milan in 313, which declared religious tolerance for Christianity in the Roman Empire, effectively ending state-sponsored persecution and paving the way for cultural acceptance. And, when the Roman Empire was united as one again in 324 with Constantine at the helm, the edict spread to include the former Eastern territories, freeing even more believers from the fear of Roman wrath.

But his contributions to Christianity didn’t stop at the political level. In 325, worried about divisions that threatened to fracture the church, he called the First Council of Nicaea. This conference of church leaders produced the Nicene Creed, a statement of faith still widely used in Christian liturgy today. His funds and decrees also led to the building of several churches, including the Church of the Holy Sepulcher at the purported site of Jesus’s tomb in Jerusalem, as well as many others.

And upon his death bed, he was baptized by Eusebius of Nicomedia, the bishop of Berytus in Phoenicia, becoming the first Roman Emperor ever baptized in the Christian Church.

Since then, debate has raged about whether Constantine was “actually” a Christian. For sure, there were flaws. Despite his vocal belief in the teachings of Jesus, he still led a life of sin not uncommon for the time and culture in which he lived. He had concubines. He oversaw executions, including those of his eldest son, his second wife, and his sister’s husband. While he ordered the destruction of pagan shrines and temples, he didn’t outlaw the practice and, some claimed, still dabbled in it himself by continuing to engage in Mithraism or sun worship. Even his understanding of the gospel may have been erroneous, as evidenced by his own baptism: he waited until death to be baptized because he believed that any sins committed in life after baptism would not be forgiven. Many historians, therefore, say Constantine’s Christianity wasn’t real. At best it was a Christian-pagan mix; at worst, it was a mere political ploy, used only to gain favor and power over his rivals.

Only God knows for sure. What is known is that Constantine saw himself, in his own words, as “the bishop of those outside the church” and believed it was his personal duty and the proper use of his imperial power to spread the gospel–and that he did. Whether it be for personal gain or not, under his leadership, Christianity spread throughout Europe and Asia. In 381, only forty-four years after his death, Christianity was made the state religion of the Roman Empire. In less than seventy years, the Christian Church went from being maligned and persecuted, the holding predominance, power, and influence within the largest, most powerful empire in the world.

Regardless of his motives, the legacy of Constantine remains the same: during his time and as a result of his influence, the message of Jesus was received and lives were changed.

Because of one man’s conversion, the world was transformed.

This, friends, is the amazing God we serve.