Atlantis: Fact or Fiction?

[Taliesin]

Possibly. I got the impression when reading it that Mithraism was a recent development in 100, and the soldiery can hardly be considered an upper class. (Soldiers were probably also the first group to worship him in a big way, I imagine, because the army was the main medium by which a faith could be spread quickly from Persia to Italy.) Hadrian was by no means representative of the upper class, either.

Also, you have to consider when looking at acceptance in popular culture that Mithraism and Christianity, though in some ways similar, were different in an important respect. The Mithraic mystery was one of blood, iron, militant brotherhood, and death, whereas the Christian one clearly is not. The former would be more familiar to the average Roman, so one expects it would be adopted and tolerated much sooner than the more foreign and subversive Christian doctrine.

Regardless, the two faiths seem to have appeared at roughly the same time.

 

[Plotinus]

Although Mithras, the Persian god, had been around for centuries, Mithraism as we know it appears to have developed at the end of the first century AD, that is, at the time Taliesin suggests. Of course the development of any religion is a gradual process, but this is the period when the earliest "Mithraist" artefacts date from. Thus, Mithraism seems to have appeared about fifty years after Christianity, if you could pin it down that precisely, which you can't.

It's important to bear in mind that in any case Christianity and Mithraism appealed to completely different kinds of people, which means that they weren't really rivals in any serious sense. A glance through Paul's letters, especially 1 Corinthians, will show that Christianity appealed especially to the lower classes, to women, and even to slaves. This continued to be the case in the second and third centuries, as the attacks on Christianity preserved in the Apologists and Origen make clear. Mithraism, by contrast, was a sort of secret society appealing to the upper middle and upper classes (inasmuch as those categories apply to Rome at this period). Soldiers, as Taliesin mentions, merchants, and so on. Women weren't even allowed to be members. Christianity, meanwhile, did not allow soldiers to be baptised, typically. So the two were really quite different in outlook and in membership, which is why the common perception of them as great rivals is really not very accurate.