Far be it from me to argue with the great man, but as I understand it that is far more than we actually know about the beliefs of Mithras, and must include a lot of postulation (it’s presumably written as theology not history)
My understanding is we know they involved fire and bulls and demigods fighting bulls, and that’s about it
That’s not what “mystery” means in this context. The mystery cults wouldn’t have been widespread if the adherents weren’t allowed to tell anyone about them.
And certainly we know much about at least one of the mystery cults, and that it was monotheistic. Christianity itself was one of those mystery cults.
Though in terms of the OP I think there is a big logical jump between saying some of these cults may have offered something that could be described as personal salvation, and saying that your average Roman in late antiquity did not believe in the traditional polytheistic Roman pantheon and instead believed in a monotheistic(ish) cult that offered them personal salvation.
Then what does it mean? It’s the central definition of mystery cults in every context I’ve read: e.g. Wikipedia:
Mystery religions , mystery cults , sacred mysteries or simply mysteries (Greek: μυστήρια), were religious schools of the Greco-Roman world for which participation was reserved to initiates(mystai) . The main characteristic of these religious schools was the secrecy associated with the particulars of the initiation and the ritual practice, which may not be revealed to outsiders
The last section of the wiki article on Roman mystery religions loosely addresses the OP. According to my reading of wiki, this is an unsettled controversy. In fact, it was somewhat controversial in ancient times: “Non-Christians in the Roman Empire in the early centuries CE, such as Lucian and Celsus, thought Christianity and the mystery cults resembled each other. Reacting to these claims by outsiders, early Christian apologists, such as Justin Martyr, denied that these cults had influenced their religion.”
Sure - I was kind of surprised that the cites went that far. It is of course hard to deduce from this distance how widespread or heartfelt something as internal as belief might be.
Archaeology is one source that speaks to geographical spread and also to sociology - e.g. Mithraism has roots in the military. We also have writings not necessarily about beliefs but e.g. people talking about how many of these blasted Isis worshippers you see nowadays, the comparison of mystery cults with Christianity etc. but compared to the evidence for e.g. belief in Christianity in 12th century France, it’s pretty thin.
Bret Devereaux covers Roman-era topics quite well in his blog, and he did a series of posts a while back on how polytheism works day-to-day (with a lot of Roman focus as that’s his area)
Interesting. So how did polytheist rituals coexist with the mystery cults? Did Mithraists still sacrifice to Neptune before a sea voyage? Or was Mithra, in effect, a one-stop-shop?
The same way such cults had always coexisted with mainstream greco-roman polytheism. “Coexisted” is not the right word they were part of mainstream greco-roman polytheism. The idea that they were this radically different thing that shared more in common with Abrahamic monotheism is not supported by the evidence IMO. The main difference in the eyes of contemporary Romans (at least the rich literate male contemporary Romans who opinions were recorded) is they were from “the East” and hence inherently not to be trusted by an honest roman.
So that’s a yes to Neptune? Would members of mystery cults still perform rituals venerating the mainstream gods, when needed, without this being seen as a paradox?
Probably? That’s the thing we know almost nothing about what followers of Mithras believed or did. It’s one the most widespread cults in later antiquity, there are temples to Mithras everywhere (particularly anywhere there was a roman military presence, as it was closely associated with the military). But we know almost nothing about it.
Of course that also means that it allows future commentators to fill in the gaps with whatever their pet theory is
Forget about its beliefs and practices. Do we know anything about its members? Can we point to a specific Roman general or governor who was known to be a Mithras follower, and who was also recorded somewhere as making sacrifices to Mars?
Also: you say that temples were built to Mithras everywhere. Were temples to other gods in these areas neglected or abandoned following their construction? This is something archeologists might be able to see.
I don’t think we can because they were so secretive but it’s likely a huge chunk of the senior military leaders (including the emperors) at it’s height were followers of Mithras. And seeing as it would have been a huge deal, and would have been commented on by contemporaries, if those senior figures had stopped sacrificing to rest of the pantheon, it’s safe to say they didn’t stop. It would have literally put the future of Rome in jeopardy in the eyes of their contemporaries (we certainly heard about it when senior Christians stopped doing so)
The Mithraists were primarily military, and they would definitely have been required to partake in the non-Mithraic military and civic religious rituals and the Imperial cult.
We also know many mithraea contained statues of other gods (eg the one in London), and inscriptions to Mithras are found at other religious sites.
The Jewish population of the early Roman Empire was substantial; per Wikipedia, some historians think it was as high as 10% of the population, although others differ. In any case, it was large enough that most Romans would certainly have heard of actual monotheism. My WAG is that there were probably a lot of monotheistic or quasi-monotheistic cults in the Mediterranean world of the early CE competing for the “monotheism sounds cool but I don’t want to mutilate my genitals” market segment, of which the Christians and Muslims eventually hit the big time.