Among the nonsense that circulates on the web is an interesting claim, which may be found in the old online Catholic Encyclopedia, and spread into atheist literature via the medium of Joseph Wheless’ Forgery in Christianity.. It is perhaps most accessible today by means of the Christ Conspiracy by a certain Acharya S., a poor woman who has seemingly managed to read uncritically incredible amounts of unreliable books, without acquiring any critical sense in the process.. The various corrupt versions of the Catholic Encyclopedia material will doubtless be professionally interesting to the textual critic, who may see therein the process of transmission by careless scribes beautifully exampled.
The CE states:
The fathers conducted the worship. The chief of the fathers, a sort of pope, who always lived at Rome, was called “Pater Patrum” or “Pater Patratus.”
We may reasonably ask what the source for this claim is. Inevitably we find that it is Franz Cumont’s Textes et Monuments, vol. 1. On p.317-8 this states:
Finally, at the top of the hierarchy were the Fathers, who appear to have presided over the sacred ceremonies (pater sacrorum). The chief of them bore the title of Pater Patrum , sometimes transformed into Pater patratus  in order to introduce an official sacerdotal title into a sect which was Roman by naturalisation. These Grand Masters of the adepts retained until their death the general control of the cult.
1. Pater patrum, cf. t. II, 535, col. 2. One became pater patrum after being an ordinary pater, cf. inscr. 14, 15 and note, and also 13 and note. — the Marcellinus leo of inscription 45 is perhaps the same person as the Domitius Marcellinus of inscr. 31. — the title of pater nomimus (inscr. 166 and note) seems to be an ordinary Father, as opposed to the Pater Patrum.
2. Pater patratus, inscr. 190; cf. however 514: Pater patratum leonem, which I cannot explain. Patratus cannot be considered as a collective, despite the expression ob honorem sacri matratus of inscription 574 b.
3. Inscr. 13 and note, 15 and note.
This material is what lies behind the statements in the C.E., which thus merely serve to popularise. (The title pater patratus is an ancient one which appears in Livy for a fetial priest with powers to make a religious oath on behalf of the Roman people to conclude treaties, so perhaps might be translated as executive father).
The material given is unsatisfactory as evidence for the large claims made. Page 535 is merely the index to all mentions of the term, 14 of them. Inscription 13 relates to CIL VI 754, set up between 357-362 A.D. by Nonius Victor Olympius, which does not seem to refer to him as a simple pater. Inscr. 14 and 15 are the monuments of Vettius Agorius Praetextatus from 387 A.D. The latter monuments certainly do not support Cumont’s claim that a Pater Patrum was first a Pater (however probable this would otherwise seem to be). Neither state, as Cumont does, that the role consisted of a general direction of the cult as a whole. Inscr. 190 is CIMRM 706, in Milan, where P. Acilius Pisonianus is labelled pater patratus, dedicates a Mithraeum with funds from the municipality of Milan after a fire. But there is no indication that this title is the same as pater patrum. Inscr. 514 is a 3rd century inscription in Spain (CIMRM 803), where presidente patrem patratum leonem, is the perfect Father of the Lions presiding.
As so often with Cumont, the evidence simply does not support the claims made in the text. Wild imagination extrapolates what might be true from the rather less exciting raw data. None of this material takes us further forward.
We can speculate ourselves. The Pater Leonem is, quite possibly, simply a pater with supervisory responsibility for the initiates of the grade of leo or Lion. By analogy, a Pater Patrum would simply be the senior pater in a Mithraeum. Given the military links of the cult, that a single individual would lead each grade, and perhaps the Mithraeum as a whole, seems inevitable, just as the centurions were led by a primus pilus in the legion. This all fits the data admirably, and gives rise to none of the exciting claims of a “Mithraic Pope”. Do we need to suppose the existence of such a figure? Even if we refer to a “High Priest of Mithras”, which might have existed … do we need to suppose that there was one? What evidence requires it? Or should we, perhaps, see in the pater patrum the equivalent of the Christian bishop, responsible for the temples in a city? We could; but what evidence requires this?
When we know nothing, it is really, really important not to speculate. The data we have indicates very little.
A useful 1982 article by Peter Herz in ZPE  lists all the monuments that refer to a Pater Patrum. There are fifteen of these in all. Eleven of these are from Rome. The majority are late Roman noblemen.
It is, in truth, a thin collection of data. I hope to review it all at some subsequent point.
-  Here. ↩
-  The passage in Wheless may be found here, apparently on p.37, who states that the CE material is on p.403-4. It reads: “The fathers conducted the worship. The chief of the fathers, a sort of pope,who always lived at Rome, was called ‘Pater Patratus’ … The members below the grade of pater called one another ‘brother,’ and social distinctions were forgotten in Mithraic unity…” ↩
-  Achrya S, The Christ Conspiracy, p.120: ‘Of Mithraism the Catholic Encyclopedia states, as related by Wheless, “The fathers conducted the worship. The chief of the fathers, a sort of pope, who always lived at Rome, was called ‘Pater Patratus.’” The Mithraic pope was also known as Papa and Pontimus Maximus.’ ↩
-  Book 1, chapter 24. Here. ↩
-  More details on the ancient “Pater patratus”, a member of the college of priests known as fetiales, may be found in William Smith’s Dictionary of Greek and Roman Antiquities (1890), online here: “It appears that when an injury had been sustained, four fetiales (Varr. ap. Non.) were deputed to seek redress, who again elected one of their number to act as their representative. This individual was styled the pater patratus populi Romani. (It is an error to suppose that the pater patratus was the permanent head of the college: Mommsen, Staatsr.2 2.670. “ ↩
-  Peter Herz, Agrestius v(ir) c(larissimus), Zeitschrift für Papyrologie und Epigraphik, Bd. 49 (1982), pp. 221-224. JSTOR. ↩