It would be hard if not outright impossible to overstate the impact Roman Emperor Constantine I had on the history of Christianity, Ancient Rome, and Europe as a whole. Best known as Constantine the Great, the kind of moniker only earned by rulers who have distinguished themselves in battle and conquest, Constantine remains an influential and controversial figure to this day. He achieved enduring fame by being the first Roman emperor to personally convert to Christianity, and for his notorious Edict of Milan, the imperial decree which legalized the worship of Christ and promoted religious freedom throughout the empire. More than 1500 years after Constantine's death, Abdu'l-Bahá, the head of the Bahá'í Faith, wrote, "His blessed name shines out across the dawn of history like the morning star, and his rank and fame among the world's noblest and most highly civilized is still on the tongues of Christians of all denominations."

Moreover, even though he is best remembered for his religious reforms and what his (mostly Christian) admirers described as his spiritual enlightenment, Constantine was also an able and effective ruler in his own right. Rising to power in a period of decline and confusion for the Roman Empire, he gave it a new and unexpected lease on life by repelling the repeated invasions of the Germanic tribes on the northern and eastern borders of the Roman domains, even going so far as to re-expand the frontier into parts of Trajan's old conquest of Dacia (modern Romania), which had been abandoned as strategically untenable.

Due to the importance of the Roman Empire and the offshoot Byzantine Empire, it's often forgotten that Constantinople wasn't chosen at random; in fact, the city already existed, and it lent its name to the empire that was subsequently centered there. Byzantium, known originally as Byzantion, was an ancient Greek city centuries before it became known as Constantinople, and the etymology of Byzantion/Byzantium is still unknown. It has been suggested that Byzantion is of Thracian origin and may be derived from the Thracian personal name Byzas, which means "he-goat."[1] Ancient Greek legend refers to King Byzas as the leader of the Megaran colonists and the founder of the city, [2] but the earliest name for a city on the site is "Lygos," which likely corresponds to an earlier Thracian settlement described by Pliny the Elder in his seminal work, Natural History: "On leaving the Dardanelles we come to the Bay of Casthenes, ...and the promontory of the Golden Horn, on which is the town of Byzantium, a free state, formerly called Lygos; it is 711 miles from Durazzo."[3]
Pliny went on to explain that Lygos was a Thracian settlement founded between the 13th and 11th centuries BCEE.[4] The site, however, was probably abandoned well before Megara founded Byzantion around 657 BCE across from Chalcedon on the Asiatic side of the Bosphorus.[5] The city was briefly renamed Augusta Antonina in the early 3rd century CE by the Emperor Septimius Severus, who razed the city to the ground in 196 CE for supporting a rival contender in the civil war and had it rebuilt in honor of his son and successor, Marcus Aurelius Antoninus, known as Caracalla.[6] This new name appears to have been quickly forgotten and abandoned, with the city reverting to Byzantium after the assassination of Caracalla in 217 CE, and that's how it would be known when Constantine fatefully moved the seat of power there over a century later.

Byzantium may have reached its zenith during the Middle Ages as Constantinople, but it had previously stood out among Greek and other ancient cities for its wealth, size, and strategic location. It is probable that given the location, if the Megarans had not founded their city where they did, another Greek polis would have.