CIMRM Supplement - Mithraeum. Ballplatz, Mainz, Germany.
CIMRM lists a couple of items from Mainz.
But in August 1976 building work in the Ballplatz square in Mainz (Roman Mogontiacum) uncovered a Mithraeum. This was outside the Roman legionary fortress.1 Unfortunately the site was destroyed without being recorded, and items from it were looted. In 2008 the materials from it were published by I. Huld-Zetsche.2 These notes are from material online.
According to the German Wikipedia article on Mogontiacum, the pottery finds dated the construction to 70-80 AD, which would make it the first such known. The overall length was 30m.3 The early date might be supported by the discovery of a temple of the Magna Mater, and also of Isis, in 1999, which was scientifically excavated and dated to the reign of Vespasian, earlier than the cult of Isis was previously known in this area. The massive deployment of troops from all over the empire is perhaps responsible.4
The finds that survived include two inscribed altars, a remarkable pottery krater with Mithraic figures, a fragment of another krater with an inscription, and an inkwell. The two altars are on a base in a covered passage on the west side of the Ballplatz.
Coordinates: 49° 59' 56" N, 8° 16' 16" E / 49.9945° N, 8.2672° E.5
From Eric Rebillard, Jorg Rupke, Group Identity and Religious Individuality in Late Antiquity, CUA, 2015, p.231:
The mithraeum in Praesenzgasse/Ballhausplatz im Mainz, which was destroyed in the course of construction work on site, belongs to the class of spectacular finds that were, unfortunately, never properly documented. Rectangular in form, it was roughly twenty-two meters long, with a three-meter-wide aisle running down the middle.42 Including the arc, measurements of which can no longer be estimated, the sanctuary would have measured some thirty meters in length, making it one of the largest sites of the Mithras cult in the Roman world.43 Findings include two Mithras altars dating to Severan times (nos. 17 and 18), two large, double-handled vessels, one of them the notable "Schlangenkrater," numerous incense chalices and clay lamps—all in all about six hundred smaller finds.44 Moreover, two altar bases are said to have been found in situ,45 The earliest ceramics date to the years of Vespasian’s reign, and the mithraeum must therefore have been in use no later than the last third of the first century A.D., making it also one of the oldest north of the alps. It underwent some changes until it was abandoned in the fourth century A.D. 44.
From Ezquerra, p.358:
The length of the cella of the ‘Ballplatz* mithraeum in Mainz, destroyed without excavation in 1976, has also been estimated at c. 30m long, though this is frankly a guess.606
And Ezquerra, p.347-8:
The now well-known Schlangengefass from the never-excavated mithraeum beneath the Ballplatz in Mainz is a slightly different matter. One face depicts in barbotine technique what seems to be a procession, moving to the left (Text-fig. 4).370 First comes a small figure wearing a cuirass, evidently a Miles, then, on a larger scale, a Pater, striding along in a stately manner, with a staff or walking stick. He is followed by an equally large figure wearing a solar crown and brandishing a whip, evidently a Heliodromus. Both of these figures wear beards. The last figure, the same size as two preceding ones (i.e. larger than the Miles), is a young man carrying a walking stick erect in the air.
A mysterious document, "The Development of the Cult of Mithras in the Western Roman Empire" on Scribd here:
... has published a fine bone ink-well from the Ballplatz Mithraeum in Mainz, rightly remarking that it shows that it was necessary in the cult’s day-to-day life to write documents which could not conveniently be kept on wax tablets -–precisely, one may think, lists of grade acquisition and membership, as well as financial records and, no doubt, liturgical texts of the kind we possess in scraps from Sta Prisca and Dura-Europos.
Altar to Mithras and Mars, dedicated by Secundinius Amantius
The first altar is marble, and dates to 151 AD – 230 AD. It is 91 cm high, 47.5 cm (Br.), 36 cm (deep). The lettering is 3.8-2.5 cm high.6 AE 1979, 425.
D(eo) I(nvicto) M(ithrae)/ et Marti/ Secundini/us Amantius/ cornicu(larius)/ praef(ecti) leg(ionis)/ XXII permi/ttente Pri/mulo patre/ ex voto pos/uit l(ibens) l(aetus) m(erito)
"To the Unconquered Sun God Mithras and Mars. Secundinius Amantius, cornicularius [=supply officer] to the prefect of the 22nd Legion, with the permission of Primulus the Pater, dedicates this willingly in fulfilment of a vow.
Altar of M. Satrius Saturninus
Broken sandstone altar, currently (77) cm H, 50cm W, 45cm D, letter size 4.7-3.2 cm. 151 AD – 230 AD.
[ ] H D D [ ]O INVICTO [ ]VATO [ ]RIVS SATVR[ ]INVS EX IVSSV POSVIT
"In honour of the temple, to the unconquered god, the Conservator, Marcus Satrius Saturninus did this by order."
Inscribed pottery fragment.
AE 2004, 1027. AE 2008, 0968.
Dated AD 120-150, this fragment of a krater contains the following inscription:
[ ]NV[ ]T M[ ] D [ ] QVINTVS CA[ ]
"To the unconquered god Mithras, Quintus Ca--- gives this gift freely."
Crater with figures
This vessel is approximately 40 cm high, 27 cm in diameter (upper rim) and dated to between 120-150 AD.
... Mithras shoots an arrow at a rock-face, from which water then gushes. 65 In this scene, Mithras is very often accompanied by two youths (occasionally by only one) wearing Phrygian caps, sometimes represented in a supplicatory gesture, or catching the water gathered in their cupped hands.66 Their identity as Cautes and Cautopates is guaranteed by one of the lines of verse from Santa Prisca.67 Until recently, there has been no indication that this particular scene played any role in Mithraic ritual. This situation was, however, dramatically changed by the discovery of a crater (a wine mixing bowl) buried under one of the floor-levels of the mithraeum in the centre of Mainz (ancient Mogontiacum, a major administrative centre of the Roman province Germania Superior).68 This cult vessel69 carries two scenes of ritual created in the expensive and difficult barbotine technique.70 One, named by Roger Beck the “Procession of Heliodromus”, can be disregarded here since it has no obvious parallel in Mithraic iconography or Mithraic myth.71 The other, however, named by Beck the “Archery of the Father”, seems to be particularly relevant to our argument. It portrays three participants in the course of a ritual. The first person, a man with full beard and a Phrygian cap sitting on a folding chair, is aiming an arrow, set to the string of a bow, at another man in front of him. This man, the initiand, is portrayed as proportionally smaller, beardless and naked; he raises his hands, which are apparently tied at the wrist, in terror to protect his face.72 Behind the naked man we can see a third person also with full beard and dressed in a tunic. In his left hand, he holds an unidentifiable object. His right hand is raised in a gesture which signals, according to the rules of ancient rhetoric, communication of important information. 73 The general identification of roles of the individual participants of this ritual is unproblematic. The sitting man with a bow is, due to his dignified appearance and the Phrygian cap he wears, to be identified as the Mithraic Father.74 The man on the right plays the role of a mystagogos pronouncing the legomena necessary to successful completion of initiation. 75 This scene plays a crucial role in our argumentation since it provides support for the hypothesis that the mythical episode of Mithras’ archery was also adapted – at least in this specific community in Mogontiacum – as a model for a ritual actually performed by local Mithraists during their cultic gatherings.76