By the fourth century CE Mithraism had spread by merchants, and through the Roman army as far North as Hadrian’s wall in Bremenium, as far West as Olisipo on the Western coast of Spain; it had permeated the Roman provinces of North Africa, and Egypt, and was thriving in its home land of Persia; stretching its influence all the way through Persia to India. As much as two percent of the population of the Roman Empire may have been initiated into the mysteries of the Cult of Mithra.
The traditional date to celebrate the birth of Mithra, going back as far as 750 BCE, is a date significant in the Roman calendar known as Saturnalius, December 25th. This date is also the celebrated birthday of such notable people as Julius Caesar, his son by adoption Augustus Caesar, the first Christian emperor, Constantine; and most famously Jesus of Nazareth himself. The fact that all of these people shared the same birth day does not constitute proof of anything regarding the relationship between Mithraism and Christianity. The Romans used a different calendar in those days, and in that time December 25th was the date of the winter solstice. It was celebrated in nearly every culture in the Northern hemisphere, as that point in the yearly cycle that the light returns and the days goes from the deepest dark to light. However, this will lead me into a discussion of some of the other tell-tale markers of the sympathetic relationship between the two faiths.
The Cult of Mithra was a “mystery religion,” meaning that it was secretive, closed to outsiders, to anyone that did not go through a significant ritual of initiation, and it purported to disclose to the initiate the mysteries of the universe. Outside of Persia, the main adherents of the Cult of Mithra were members of the Roman army. There is no evidence that Mithraites were ever persecuted as Christians were; at times, but like a number of other closed societies in ancient Rome they had to keep to themselves, and guard their secrets. The necessity of secrecy for the cult of Mithra, as with that of many other cults, had much to do with the paranoid mindset of the Roman emperors. All manner of private groups, trade guilds, and burial societies, were periodically outlawed by one emperor or another; this on account of the fact that most of the emperors were insecure in their power, and constantly suspicious of treason, and sedition. The fact that the Cult of Mithra recruited many of its members from the army probably spared it from persecution because the emperors always ruled by fragile alliances, and loose coalitions. They were always dependent on the power of the armies to keep them in the seat of power. If the emperors were to alienate large groups of their supporters (the army) through a persecution of their faith they would lose that power.
As I noted earlier Ulansey saw the secrecy of the cult of Mithra, as practiced in the Roman Empire as something distinct from the Persian form of Mithraism. There are differences between the two systems of belief, but so great as to merit the claim that they are distinct from one another. A close look at the structure of these religious systems, icons, rituals and beliefs will reveal that relationship, and also the close relationship Mithraism has with Christianity.