precession.
We have two possible clues as to what the "secrets" were:
Porphyry (c. 234 – c. 305 AD) wrote that the mithraeum functioned as the place of initiation into a mystery of the “descent and exit of souls” and that it was designed and equipped for this purpose as a “likeness of the universe. The things which the cave contained, by their proportionate arrangement, provided [the] symbols of the elements and climates of the cosmos.
And:
Georgius Cedrenos (fl. 11th century), wrote:
Perseus, they say, brought to Persia initiation and magic, which by his secrets made the fire of the sky descend; with the aid of this art, he brought the celestial fire to the earth, and he had it preserved in a temple under the name of the sacred immortal fire; he chose virtuous men as ministers of a new cult, and established the Magi as the depositors and guardians of this fire which they were charged to protect.
Concerning the “descent and exit of souls” from the above (and possibly virtuous men as ministers), Hall makes reference to the Mithra initiation:
The rites of Mithras were performed in caves. Porphyry, in his Cave of the Nymphs, states that Zarathustra (Zoroaster) was the first to consecrate a cave to the worship of God, because a cavern was symbolic of the earth, or the lower world of darkness. John P. Lundy, in his Monumental Christianity, describes the cave of Mithras as follows:
"But this cave was adorned with the signs of the zodiac, Cancer and Capricorn. The summer and winter solstices were chiefly conspicuous, as the gates of souls descending into this life, or passing out of it in their ascent to the Gods; Cancer being the gate of descent, and Capricorn of ascent. These are the two avenues of the immortals passing up and down from earth to heaven, and from heaven to earth."
The so-called chair of St. Peter, in Rome, was believed to have been used in one of the pagan Mysteries, possibly that of Mithras, in whose subterranean grottoes the votaries of the Christian Mysteries met in the early days of their faith. In Anacalypsis, Godfrey Higgins writes that in 1662, while cleaning this sacred chair of Bar-Jonas, the Twelve Labors of Hercules were discovered upon it, and that later the French discovered upon the same chair the Mohammedan confession of faith, written in Arabic.
Initiation into the rites of Mithras, like initiation into many other ancient schools of philosophy, apparently consisted of three important degrees. Preparation for these degrees consisted of self-purification, the building up of the intellectual powers, and the control of the animal nature. In the first degree the candidate was given a crown upon the point of a sword and instructed in the mysteries of Mithras' hidden power. Probably he was taught that the golden crown represented his own spiritual nature, which must be objectified and unfolded before he could truly glorify Mithras; for Mithras was his own soul, standing as mediator between Ormuzd, his spirit, and Ahriman, his animal nature. In the second degree he was given the armor of intelligence and purity and sent into the darkness of subterranean pits to fight the beasts of lust, passion, and degeneracy. In the third degree he was given a cape, upon which were drawn or woven the signs of the zodiac and other astronomical symbols. After his initiations were over, he was hailed as one who had risen from the dead, was instructed in the secret teachings of the Persian mystics, and became a full-fledged member of the order. Candidates who successfully passed the Mithraic initiations were called Lions and were marked upon their foreheads with the Egyptian cross. Mithras himself is often pictured with the head of a lion and two pairs of wings. Throughout the entire ritual were repeated references to the birth of Mithras as the Sun God, his sacrifice for man, his death that men might have eternal life, and lastly, his resurrection and the saving of all humanity by his intercession before the throne of Ormuzd. (See Heckethorn.)
Now, the other thing that occurred to me, and I have not looked into this at all, but it is interesting that down through history, the image that we're given for "evil" is often accompanied by horns, and I was wondering if this was perhaps by design, in the same vein of Mithraism.
Curiously, with a point on the Bull's horns, moreover the struggle between good an evil (Ahriman) comes up here (again by Hall):
When Ormuzd created the earth, Ahriman entered into its grosser elements. Whenever Ormuzd did a good deed, Ahriman placed the principle of evil within it. At last when Ormuzd created the human race, Ahriman became incarnate in the lower nature of man so that in each personality the Spirit of Good and the Spirit of Evil struggle for control. For 3,000 years Ormuzd ruled the celestial worlds with light and goodness. Then he created man. For another 3,000 years he ruled man with wisdom, and integrity. Then the power of Ahriman began, and the struggle for the soul of man continues through the next period of 3,000 years. During the fourth period of 3,000 years, the power of Ahriman will be destroyed. Good will return to the world again, evil and death will be vanquished, and at last the Spirit of Evil will bow humbly before the throne of Ormuzd. While Ormuzd and Ahriman are struggling for control of the human soul and for supremacy in Nature, Mithras, God of Intelligence, stands as mediator between the two. Many authors have noted the similarity between mercury and Mithras. As the chemical mercury acts as a solvent (according to alchemists), so Mithras seeks to harmonize the two celestial opposites.
Of the Horns (modification of [T]horn eg. the crown of thorns representing the suffering of the soul):
In ancient Egypt it was during this period--when the vernal equinox was in the sign of Taurus--that the Bull, Apis, was sacred to the Sun God, who was worshiped through the animal equivalent of the celestial sign which he had impregnated with his presence at the time of its crossing into the Northern Hemisphere. This is the meaning of an ancient saying that the celestial Bull "broke the egg of the year with his horns.
Concerning Egyptian cosmology specifics and the Bull:
Sampson Arnold Mackey, in his Mythological Astronomy of the Ancients Demonstrated, makes note of two very interesting points concerning the bull in Egyptian symbolism. Mr. Mackey is of the opinion that the motion of the earth that we know as the alternation of the poles has resulted in a great change of relative position of the equator and the zodiacal band. He believes that originally the band of the zodiac was at right angles to the equator, with the sign of Cancer opposite the north pole and the sign of Capricorn opposite the south pole. It is possible that the Orphic symbol of the serpent twisted around the egg attempts to show the motion of the sun in relation to the earth under such conditions. Mr. Mackey advances the Labyrinth of Crete, the name Abraxas, and the magic formula, abracadabra, among other things, to substantiate his theory. Concerning abracadabra he states:
"But the slow progressive disappearance of the Bull is most happily commemorated in the vanishing series of letters so emphatically expressive of the great astronomical fact. For ABRACADABRA is The Bull, the only Bull. The ancient sentence split into its component parts stands thus: Ab'r-achad-ab'ra, i. e., Ab'r, the Bull; achad, the only, &c.--Achad is one of the names of the Sun, given him in consequence of his Shining ALONE,--he is the ONLY Star to be seen when he is seen--the remaining ab'ra, makes the whole to be, The Bull, the only Bull; while the repetition of the name omitting a letter, till all is gone, is the most simple, yet the most satisfactory method that could have been devised to preserve the memory of the fact; and the name of Sorapis, or Serapis, given to the Bull at the above ceremony puts it beyond all doubt. * * * This word (Abracadabra) disappears in eleven decreasing stages; as in the figure. And what is very remarkable, a body with three heads is folded up by a Serpent with eleven Coils, and placed by Sorapis: and the eleven Volves of the Serpent form a triangle similar to that formed by the ELEVEN diminishing lines of the abracadabra."
Never thought of that word and what it possibly meant.