The Zeitgeist stuff seems to be drawn from Kersey Graves' 1875 work on Sixteen Crucified Savior Gods. Seeing as how Franz Cumont, the scholar who did the first really serious work on Mithraism in the Roman Empire, was a mere boy at the time and did not publish until the early 20th century it is hard to know what value Graves' sources might have been. The Roman Mithraic cult morphed into the Cult of Sol Invictus (the All-Conquering Sun) and that clay-footed xtian hero, Constantine, kept him on his coinage throughout his life.
Mithras/Sol Invictus was a true mystery cult. They had no writings and the knowledge was passed from master to apprentice verbally. All we can tell from excavating the various Mithraeums which have been found is that the wall paintings stress the killing of the celestial bull by Mithras. You gotta admit....that's something. Beats getting your fucking ass nailed to a cross.
Mithras/Sol Invictus was a true mystery cult. They had no writings and the knowledge was passed from master to apprentice verbally. All we can tell from excavating the various Mithraeums which have been found is that the wall paintings stress the killing of the celestial bull by Mithras. You gotta admit....that's something. Beats getting your fucking ass nailed to a cross.