Mithraism, the cult mainly embraced by the Roman legions, centered around the worship of the god Mithras and the Mithraic mysteries. This deity that originated from the Indian-Persian god Mithra, who was worshipped by four religions: in Hinduism (as Mitra), in Zoroastrianism (as Mithra), in Manichaenism (as Mithra), and the Roman Mithraic mysteries (as Mithras).
The cult was first evident toward the end of the first century AD. Being popular among the military its locations were seen in the frontier regions around the Danube, the Rhine, and Hadrian’s Wall in Northern England.
However, there were also civilian temples, notably in Italy, especially in Ostia, the port city of Rome. The cult eclipsed in the fifth century due to the rise of Christianity. It is difficult to reconstruct the Mithraic belief and practice because no specifically Mithraic texts survived, only inscriptions and accounts by outsiders such as Porphyry.
The major source of evidence is hundreds of excavated temples (Mithraea) and their statuary. The cult explicitly claimed to have been founded by Zoroaster and became known as the Persian mysteries. There were seven grades of initiation, each under the protection of a planet: Raven (Mercury), Bride (Venus), Soldier (Mars), Lion (Jupiter), Persian (moon), Runner of the Sun (sun), Father (Saturn). Progression through the grades was thought to reflect the soul’s progress through the planetary spheres, and it probably reflected deeper esoteric knowledge.
The main cult relief (tauroctony) depicted Mithras slaying the bull, a scene thought to have soteriological significance, understood at least in part in astrological terms. Other scenes depicted Mithras and Sol banqueting in what was the mythic prototype of the community ritual meals of bread and wine. The death of the bull and the ritual meal were depicted as occurring in a cave, and the temple structure were commonly made cave-like to emphasize the cosmological significance of the acts within. Side scenes of the temple show Mithras being born from a rock, (he was known as Mithras Petrogenes).
Some of the popular texts state that the cult included the rite of taurobolium in which an initiate descended into a pit over which a bull was slain and in whose blood the initiated bathed. This could not have been practiced in Mithraism, because virtually all known temples were too small for a bull to enter. The death of the bull, therefore, appears to have been thought of as a unique inimitable act of the god himself, who is described in one inscription as having saved the initiates by the shedding of the eternal blood.
Mithraism appears from the inscriptions to have been a very respectable cult, inculcating a disciplined ascetic, and arduous life. The cult is interesting in and of itself, as a mystery cult, and because of some of the paralleled concepts that it shared with emerging Christianity. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, «Mithra,» pp. 647-648