A Brief History
According to Orthodox Christian tradition, on October 27, 312, the night before the Battle of Milvian Bridge against the Roman Emperor Maxentius, the Emperor Constantine the Great adopted as his motto the Greek phrase “ἐν τούτῳ νίκα” after having a vision of a Christogram in the sky.
This is one of the most unusual and controversial stories in the history of Christianity, and probably the only time the Christian religion was involved so energetically in the military battlefield. Of course nothing can be officially proved, and this story is a matter of faith most of all, but the life of Constantine the Great and the story of this incident can be examined a little more closely.
Constantine was the emperor who transferred the capital of the Byzantine Empire from Rome to Constantinople, laying the foundation for the transformation of the Empire from a Roman state to a Greek one. He was the first Christian emperor, the first ruler to adopt the religion that would go on to dominate the entire Byzantine Empire – Orthodox Christianity. In most Orthodox Christian countries such as Greece, Russia, and Romania he is considered a saint equal to the twelve Apostles.
One of the keys to achieving all this was the Battle of the Milvian Bridge against the Roman Emperor Maxentius on 28 October 312, a victory for Constantine forever linked with his famous vision – a luminous cross in the sky that took the form ☧, from the Greek letters Chi and Rho (X and P), the first two letters of the name “Christ” in Greek. The Christogram in the sky bore the inscription «᾿Εν Τούτῳ Νίκα» [Latin: In hoc signo vinces; English: In this sign you will conquer].
Over the years, many historians have tried to provide a scientific account of the vision of Constantine, but without any significant success. According to psychological interpretations of this event, Constantine, while he could not know that the outcome of the battle would determine the future of Europe as a whole, certainly did realize how decisive was the upcoming clash for his Byzantine Empire. Therefore, many historians try to explain his vision from a psychological point of view, claiming that the vision was nothing more than an illusion caused by his excessive anxiety and stress about the outcome of the battle. Other historians, appealing to the findings of astronomy, note that the positions of the planets on that day formed an X and a P cruciform alignment. So they suggest that the vision Constantine saw that evening was nothing more than an astronomical phenomenon. Of course the Orthodox Church, which honors the great Constantine as a saint equal to the Apostles, insists that the vision was a miracle, a divine sign from God.
Whatever the truth, the historical fact remains that Constantine experienced something significant enough to lead him to a historic decision shocking for its time. To insure the victory foretold in his vision – “In this sign you will conquer,” he had the Roman legions replace the pagan gods on their shields with standards bearing red banners with the Chi (χ)-Rho (ρ) monogram ☧. This banner, called a labarum, was hung suspended from the crossbar, making it an excellent symbol for the crucified Christ.
Because it was too difficult and too costly, the coins of the time did not bear the new symbol. But a new era had begun, and Constantine adopted the monogram as his own, eventually even topping his Byzantine crown with the Christogram whose appearance in the sky led him to victory.
For more information about Constantine and a deeper look at this particular incident, you can read The Life and Times of Constantine the Great by D. G. Kousoulas.
If you fancy a more religious view of the topic, you should check out Constantine the Great: And the Christian Revolution by G. P. Baker.