Orphic speculation influenced the cult of Mithras at times. In Orphism, Phanes emerged from the world egg at the beginning of time, bringing the universe into existence.
There is some literary evidence of the syncretism of Mithras and Phanes. A list of the eight elements of creation appears in Zenobius and Theon of Smyrna; most of the elements are the same, but in Zenobius the seventh element is 'Mithras', in Theon it is 'Phanes'.
A Greek inscription on a statue base from a Mithraeum in Rome reads "to Deus Sol Mithras Phanes". A relief from Vercovium (Housesteads) on Hadrian's Wall shows Mithras emerging from the cosmic egg, which is represented both as such and by the shape of the zodiacal ring. Ulansey adds:
"The identification between Mithras and Phanes indicated by CIMRM 860 is also explicitly attested by an inscription found in Rome dedicated to 'Zeus-Helios-Mithras-Phanes' and another inscription dedicated to 'Helios-Mithras-Phanes'."
Another syncretistic relief is in Modena. This shows Phanes coming from an egg with flames shooting out around him, surrounded by the twelve signs of the zodiac, in an image very similar to that at Newcastle. Further references also exist.
Mithras stock epithet is sol invictus, "invincible sun". However, Mithras is distinct from both Sol and Sol Invictus, and they are separate entitites on Mithraic statuary and artwork such as the tauroctony scenes, in Mithras hunting scenes, and in the Mithraic banquet scenes in which Mithras dines with Sol. Other scenes feature Mithras ascending behind Sol in the latter's chariot, the deities shaking hands and the two gods at an altar with pieces of meat on a spit or spits. One peculiar scene shows Sol kneeling before Mithras, who holds an object, interpreted either as a Phrygian cap or the haunch of the bull, in his hand.
Different gods being each other is a feature of Hellenistic syncretism however and the distinct imagery sometimes is intended to convey such ideas. Mithras shaking hands with Helios affirms their identity as the same underlying deity.
Unlike Helios/Sol, who was part of the traditional state-sponsored Roman religious system, and also unlike the Sol Invictus cult, which became an official state-sponsored cult in 274 under Aurelian, the Mithraic cult (as all other mystery cults) did not receive state sanction. Under Commodus rule (r. 180-192 AD), the title invictus became a standard part of imperial titulature, but this was an adoption from Hercules Invictus, not from either Sol or Mithras.
The Mithraea at Carnuntum appear to have been constructed in close association with contemporary temple of Jupiter Dolichenus, and there seem to have been considerable similarities between the two cults; both being mystery cults with secret liturgies, both being popular in the military, and having similar names for their officials and initiates. Two large Mithrea have been discovered in Doliche itself (modern Gaziantep in Turkey), which have been proposed as being unusually early.
The idea of a relationship between early Christianity and Mithraism is based on a remark in the 2nd-century Christian writer Justin Martyr, who accused the Mithraists of diabolically imitating the Christian communion rite. Based upon this statement, Ernest Renan in 1882 set forth a vivid depiction of two rival religions: "if the growth of Christianity had been arrested by some mortal malady, the world would have been Mithraic." Scholar Edwin M. Yamauchi criticized Renan's inference, which he claimed, "published nearly 150 years ago, has no value as a source. He [Renan] knew very little about Mithraism."
Christian apologists, among them Ronald Nash and Edwin Yamauchi, have suggested a different interpretation of Mithraism's relationship to Christianity. Yamauchi, pointing out that most of the textual evidence for Mithraist doctrine was written after the New Testament was in broad circulation, posits that it is more likely that Mithraism borrowed from Christianity than the other way around.
The philosopher Celsus in the second century provides some evidence that Ophite gnostic ideas were influencing the mysteries of Mithras.
It is said that the birth of Mithras was a virgin birth, like that of Jesus. David Ulansey speculates that this was a belief derived from the Perseus myths, which held he was born from an underground cavern. In reality, Mithras was born from a rock as stated in miraculous birth article.
It is often stated that Mithras was thought to have been born on December 25. But Beck states that this is not the case. In fact he calls this assertion "that hoariest of 'facts'". He continues: "In truth, the only evidence for it is the celebration of the birthday of Invictus on that date in Calendar of Philocalus. Invictus is of course Sol Invictus, Aurelian's sun god. It does not follow that a different, earlier, and unofficial sun god, Sol Invictus Mithras, was necessarily or even probably, born on that day too."
Unusually amongst Roman mystery cults, the mysteries of Mithras had no 'public' face; worship of Mithras was confined to initiates, and they could only undertake such worship in the secrecy of the Mithraeum. Clauss states: "the Mithraic Mysteries had no public ceremonies of its own. The festival of natalis Invicti [Birth of the Unconquerable (Sun)], held on 25 December, was a general festival of the Sun, and by no means specific to the Mysteries of Mithras.".
Steven Hijmans has discussed in detail whether the general natalis Invicti festival was related to Christmas but does not give Mithras as a possible source.
A painted text on the wall of the St. Prisca Mithraeum (c A.D. 200) in Rome contains the words: et nos servasti (?) . . . sanguine fuso (and you have saved us ... in the shed blood). The meaning of this text is unclear, although presumably it refers to the bull killed by Mithras, as no other source refers to a Mithraic salvation. However, the servasti is only a conjecture. According to Robert Turcan, Mithraic salvation had little to do with the other-worldly destiny of individual souls, but was on the Zoroastrian pattern of man's participation in the cosmic struggle of the good creation against the forces of evil.
Monuments in the Danube area depict Mithras shooting a bow at a rock in the presence of the torch-bearers, apparently to encourage water to come forth. Clauss states that, after the ritual meal, this "water-miracle offers the clearest parallel with Christianity".
Tertullian states that followers of Mithras were marked on their forehead in an unspecified manner. There is no indication that this mark was made in the form of a cross, or a branding, or a tattoo, or a permanent mark of any kind. The symbol of a circle with a diagonal cross inscribed within it is commonly found in Mithraea, especially in association with the Leontocephaline figure.
From the end of the 18th century some scholars have suggested that certain elements in medieval Christian art reflect images found in Mithraic reliefs. Franz Cumont was among these scholars, although he studied each motif in isolation rather than in context. Cumont suggested that after the triumph of the Christian church over paganism, artists continued to make use of stock images originally devised for Mithras in order to depict the new and unfamiliar stories of the bible. The "stranglehold of the workshop" meant that the first Christian artworks were heavily based on pagan art, and "a few alterations in costume and attitude transformed a pagan scene into a Christian picture".
A series of scholars have since discussed possible similarities with Mithraic reliefs in medieval Romanesque art. Vermaseren stated that the only certain example of such influence was an image of Elijah drawn up to heaven in a chariot drawn by fiery horses. Deman stated that to compare isolated elements was not useful, and that combinations should be studied. He also pointed out that a similarity of image does not tell us whether this implies an ideological influence, or merely a tradition of craftmanship. He then gave a list of medieval reliefs that parallel Mithraic images, but refused to draw conclusions from such parallels, since these would be subjective.
Several of the best preserved Mithraea, especially those in Rome such as at San Clemente and Santa Prisca, are now to be found underneath Christian churches. It has been suggested that these instances might indicate a tendency for Christians to adopt Mithraea for Christian worship, in a similar manner to the undoubted conversion into churches of temples and shrines of civic paganism, such as the Pantheon. However, in these Roman instances, the Mithraeum appears to have been filled with rubble prior to the erection of a church over the top; and hence they cannot be considered demonstrable examples of deliberate re-use. A study of early Christian churches in Britain concluded that, if anything, the evidence there suggested a tendency to avoid locating churches on the sites of former Mithraea.
On the other hand, there is at least one known example of a Mithraic carved relief being re-used on a Christian church, in the early 11th-century tower added to the church of St Peter at Gowts in Lincoln, England. A much-weathered Mithraic lion-headed figure carrying keys (presumably from a ruined Mithraeum in Roman Lincoln) was incorporated into the church tower, apparently in the mistaken belief that it was an ancient representation of the Apostle Peter. Elsewhere, as in one of the Mithraea in Doliche, there are instances where the tauroctony of a cave Mithraeum has been replaced by a cross, which suggests later use as a church; but again the date of re-use cannot be determined, and hence it is by no means certain how far the Christian occupiers were aware of their cave's Mithraic past.