A “typical” mithraeum

Many so-called Greco-Roman mystery cults involved some form of public ritual, such as festivals and processions. The cult of Magna Mater had the Megalesia, the cult of Isis had the Navigium Isidis, and the Eleusinian Mysteries had both the Epidauria and the procession to the Eleusinion.Footnote ⁷ In contrast, the cult of Mithras was almost unique in the extent of its inward focus.Footnote ⁸ There is no evidence that the cult engaged in any public events, with all Mithraic rituals apparently conducted inside mithraea.Footnote ⁹ The other aforementioned so-called mystery cults also had large, ostentatious temples that often contained at least some areas open to the public.Footnote ¹⁰ Mithraea, by contrast, were usually relatively small, with space to hold only 50 initiates or fewer, and entry was presumably limited to members of the cult. There is also no evidence for mithraea with elaborate exterior decoration, suggesting this was considered of little consequence.Footnote ¹¹

Mithraea first appear in the archaeological record around the late 1st c. CE.Footnote ¹² From this time until the late 3rd c., the inner chambers of mithraea largely adhere to a set ground plan, regardless of their size or location: a central aisle flanked by parallel benches that terminated in front of a niche or plinth where the cult image of Mithras stabbing the bull (the “tauroctony”) was placed (Figs. 1–2).Footnote ¹³ The ceiling would usually take the form of a vault and was sometimes decorated to be rock-like in appearance. These rooms were usually windowless and artificially lit using candles and oil lamps. The intention of this design was to create a cave-like atmosphere; this was made explicit in Italy, where mithraea were typically referred to in inscriptions as spelaea (caves).Footnote ¹⁴ In some instances, mithraea were installed in actual caves or attached to rock faces, into which the cult niche or the tauroctony itself would be carved, although the majority were constructed as standalone buildings or installed within pre-existing structures such as private houses, bath-complexes, or public buildings.

Fig. 1. Plan of a typical mithraeum. (D. Walsh.)

Fig. 2. Extant mithraea that exhibit the typical plan: (clockwise from top-left): Aquincum II, Carrawburgh, London (original plan), and the Mithraeum of the Serpents at Ostia. (Photographs by D. Walsh.)

According to Roger Beck, the inner chamber was not intended to be seen as a cave alone; rather, the “cave” served as an allegory of the cosmos. Beck's model draws on the account of the 3rd-c. philosopher Porphyry:

How this star-map was projected onto the inner chamber of the mithraeum and the role this played in Mithraic rituals has been discussed at length in various publications by Beck and Richard Gordon.Footnote ¹⁶ There is not the space here to delve into the complexities of these hypotheses, but a basic outline is required. The cave has sometimes been used as an allegory of the cosmos due to its (idealized) shape: if one stands in a cave and imagines that the domed roof above them is reflected below their feet then they would be standing at the center of a sphere, which is the shape of the cosmos. Having created a cave-like space inside the mithraeum, a map of the cosmos was then projected onto this space via the arrangement of fixtures (the benches, aisle, niches, etc.) and symbols (the cult image, depictions of the torchbearers, signs of the Zodiac, representations of the planets, etc.). Thus, to move across the mithraeum was to move across the cosmos.Footnote ¹⁷

According to Beck, this map of the cosmos played an important role in Mithraic initiations. These initiations evidently varied in their details across space and time but were usually intensive processes, with the initiate, stripped, blindfolded and with hands bound, brought before the head of the Mithraic community: the Father. As part of the ritual the initiate would “die” and be “reborn” as a member of the congregation, and in Beck's model, the topography of the inner chamber of a mithraeum created a pathway for their souls to ascend and descend through the cosmos.Footnote ¹⁸ In this model, initiates underwent several initiations as they advanced through the various Mithraic grades, with the ritual somewhat different each time. As each new grade was attained, so too was a greater understanding of the Mithraic Mysteries, with the initiate progressing through seven planetary spheres that were linked to each grade (from lowest to highest: Raven/Mercury, Nymph/Venus, Soldier/Mars, Lion/Jupiter, Persian/Luna, Sun-Runner/Sol, and Father/Saturn).

However, while the basic premise of a windowless room consisting of a bench-aisle-bench plan that served as a general representation of the cave/cosmos could be easily understood and repeated (particularly given the relative ease with which it could be constructed), caution must be urged in assuming that all mithraea were designed with the intention of containing a detailed star-map. Moreover, even in cases where the original design of the mithraeum did contain a star-map, this may not have been consistently understood by subsequent generations of Mithraic worshippers, particularly without texts to guide them. We must also remember that Mithraic communities were not all (and were perhaps even rarely) populated by men with a detailed understanding of and interest in astrology. Certainly, while mithraea constructed across the 2nd to 3rd c. adhere to a set plan, there is often variation in how they were furnished and decorated, and many have not produced any evidence of astrological symbolism.Footnote ¹⁹ As Gordon has argued, while there was evidently a Mithraic rubric that the community's founder was expected to follow (e.g., the tauroctony, the “typical” mithraeum design, the Father as the leader of the community, etc.), there was ample scope to execute this in a way that reflected the varied beliefs and aims of each Mithraic community who made a bricolage of ideas, rituals and imagery circulating at the time.Footnote ²⁰

While there may have been considerable variety in how the interior of mithraea were understood on a symbolic level, there was evidently consistent practical use of them as dining spaces.Footnote ²¹ Feasting was clearly a common Mithraic ritual, as large faunal assemblages have been found in and around many mithraea, often including concentrations of poultry and adolescent pig.Footnote ²² Drinking was also a prominent aspect of such events, with ceramic drinking vessels often bearing inscriptions in honor of Mithras.Footnote ²³ Feasts were perhaps held to consecrate mithraea, and probably took place following initiations and to mark certain events in relation to the movement of celestial bodies (such as the solstice).Footnote ²⁴ The feast of Sol and Mithras depicted in several reliefs also appears to have been re-enacted by the initiates, with the Sun-Runner and the Father acting as surrogates for the deities respectively.Footnote ²⁵ It is unlikely that participants in these feasts were seated at random. The Father and Sun-Runner perhaps sat closest to the cult relief, maybe in the center of the aisle, echoing the placement of their icons in the Felicissimus mithraeum, while the other grades would then recline on the benches in an order befitting their grade seniority and/or perhaps the required position of their related planet.Footnote ²⁶ As Anja Klöckner has observed, the tauroctony (and by extension the Father and perhaps Sun-Runner) occupied the central position during these feasts not only in terms of space, but also in terms of value and prestige, for it was correct Roman table etiquette that the guest of honor should take the central place in the triclinium.Footnote ²⁷

To summarize, the design of the mithraeum served three roles: A) a dining room; B) a replica of the cave in which the tauroctony takes place; and C) perhaps a map of the cosmos, to which Mithras's sacrifice gave birth and through which the souls of the initiates could ascend and descend. Of these, the reasons for A and B would be self-explanatory to any Mithraic initiate. In contrast, C is more complex and arguably would be the hardest to sustain a consistent and nuanced understanding of across multiple generations. The general idea that the cave symbolized the cosmos could perhaps be maintained, but that it was intended as a detailed “star-map” seems a more difficult proposition. Additionally, A and C would be most affected by an alteration to the bench-aisle-bench layout, such as the removal of one or both benches, for this would alter the seating arrangements of the feast (including the position of Mithras) and so have an impact on the experience of the participants. It would also now be impossible to conceive of the space as a star-map. Such changes might also have an impact on initiation rituals, with mithraea no longer able to facilitate an initiate's ascent and descent through the heavens. Of course, as noted, given the complexities of the star-map model, it is possible that in many Mithraic communities this “movement of the soul” was not part of the initiation process. What we can say with certainty, however, is that initiations which did involve this aspect could not have occurred in mithraea with atypical plans.

Mithraea with atypical plans

In multiple locations across the Roman Empire, mithraea appear from the late 3rd to 4th c. that do not adhere to the typical bench-aisle-bench plan (Fig. 3). At Hawarte in Syria, a mithraeum was installed in a cave that was accessed from the south by several steps.Footnote ²⁸ The inner chamber (6.45–7.20 × 4.80 m) lay in the northeast corner of the cave and was partitioned off from the rest of the space by man-made stone walls. The mithraeum appears to date to the end of the 3rd c., and in the mid-4th c. it underwent alterations when a podium was added in front of a niche and the first of five layers of painting covered the walls of both the ante- and inner chambers.Footnote ²⁹ In the inner chamber there were benches running along the east and south walls (ca. 6.86 m N–S and 4.04 m E–W). No sculptures or reliefs were found in the mithraeum, but a niche in the north wall of the inner chamber presumably once held such an item.

Fig. 3. Comparative plan of atypical mithraea. (D. Walsh.)

Many of the extant paintings at Hawarte, which are part of the fifth and final composition that likely dates to the early 5th c., exhibit a mix of typical Mithraic iconography along with some images which are highly unusual. The north wall of the antechamber was decorated with scenes of dark-skinned individuals being eaten by lions, while flanking the entrance to the inner chamber are depictions of two figures standing in front of white horses. The better preserved of these two horsemen holds a short, two-headed, dark-skinned figure by a chain.Footnote ³⁰ In the inner chamber, beginning to the right of the niche a continuous frieze can be followed around the room that depicts: 1) Zeus battling snake-headed monsters; 2) Mithras emerging from the rock; 3) Mithras in a cypress tree with Sol looking on; 4) the tauroctony above symbols of the seven Mithraic grades; 5) Sol kneeling before Mithras; 6) a mounted hunter (Mithras?) chasing deer, a boar, and a panther; and 7) a city wall adorned with demonic heads with rays of light descending on them. The interpretation of, and the inspiration behind, the paintings of the hunting scenes, the riders, and the heads lining the top of a fortification has been cause for debate, with suggestions that these images drew on Zoroastrian and Manichean concepts.Footnote ³¹ It is not within the scope of this paper to discuss these interpretations, but given these unusual images, this was evidently a Mithraic community that had been influenced by other religious movements operating in this region.

It is also noteworthy that the painting of the tauroctony at Hawarte does not conform to the typical placement in relation to the benches, as it is above the longer bench on the eastern wall. However, the image does face the entrance to the chamber, as is usually the case in mithraea. It has been suggested that the cult niche would have held another image of the tauroctony, but this is problematic as it would create two distinct focal points in the mithraeum.Footnote ³² In other cases when more than one tauroctony was present, they were generally placed together, seemingly to avoid such a problem, as was the case at Dura-Europos, Poetovio, the Castra Peregrinorum in Rome, and Vulci.Footnote ³³ Difficulties remain even if the image placed in the niche was not a depiction of the tauroctony. While the mithraeum contained an unusual bench arrangement and iconography, this Mithraic community appears to have practiced ritual feasting in a manner similar to their counterparts elsewhere, as the faunal assemblage contained a relatively high concentration of chicken bones, although pig bones were only found in small quantities.Footnote ³⁴ It is perplexing that those participants in these feasts who sat on the bench along the east wall would face away from Mithras while they ate. The only explanation is that the Father, and possibly Sun-Runner, occupied this bench, given that they usually appear to have sat in front of the tauroctony in other Mithraic communities. As this is the longer bench, however, it presumably accommodated several people. Based on the available evidence it is difficult to explain the arrangement of this mithraeum.

The position of the tauroctony in relation to the benches would also be problematic in mithraea that contained just a single bench. In Dalmatia, the mithraea at Konjic and Jajce have each produced evidence for only a single bench; in both cases this was positioned to the viewer's left when facing the tauroctony.Footnote ³⁵ Both were constructed in the late 3rd to early 4th c., although Konjic (9.00 × 5.00 m) was a free-standing structure, while Jajce (7.00 × 2.80 m) was built against a rock face onto which the tauroctony was carved. At Konjic, the excavators suggested that another bench might have existed, but no evidence of it has been found. The approximate findspot of an altar in the southeast corner also provides an obstacle to this interpretation, as this would have encroached on where the bench stood. Again, both mithraea produced evidence for ritual feasting, although to what extent these faunal assemblages resembled those found in other mithraea is unclear.Footnote ³⁶ In any case, the position of the tauroctony to the left of the participants would not put Mithras in pride of place during the event.

The 4th-c. Mithraeum of the Colored Marbles at Ostia, currently the latest of the ca. 20 mithraea found in the town, also contained a single bench.Footnote ³⁷ In the mid-4th c., the mithraeum was installed in a room attached to a former tavern, and it remained in use until the 5th c. It is possible that the whole building had been converted for cultic use at this time, with objects identified as an Isaic “crown” and the handle of a possible sistrum found inside. Graffiti interpreted as depicting the Navigium Isidis festival and another that states “To the unconquered god Mithras and to the great god Kronos” were present in the central room. The mithraeum was at a lower level than the rest of the building and was accessed by stairs from the southwest. A well, which contained fragments of ceramics usually used as tableware and storage vessels, was also present in the inner chamber.Footnote ³⁸ The floor was decorated with opus reticulatum (hence the name of the mithraeum), while the walls were painted in a basic manner designed to emulate marble. It measured 7.2 × 3 m and could accommodate around 12 people. At the far end of the chamber was a niche, presumably intended to hold an image of the tauroctony. In contrast to the mithraea at Konjic and Jajce in Dalmatia, the bench was to the viewer's right when facing the tauroctony, although again the same problem arises: the image of Mithras would not have taken center-stage; rather, it would be relegated to the periphery during cult meals.

There are also mithraea that have not produced any evidence for benches.Footnote ³⁹ In Rome, no benches were found in the small (3.7 × 2.4 m) early-4th-c. mithraeum at Via Giovanni Lanza 128.Footnote ⁴⁰ It was installed in what appears to have been a storage room in an affluent 4th-c. house. It contained a small tauroctony sat on a shelf with an upside-down column base underneath it that presumably served as an altar. The entrance to the mithraeum lay behind a small lararium, also from the 4th c., which contained a large statue of Isis-Fortuna, along with smaller images of the Lares, Serapis, Hercules, Horus-Harpocrates, Aphrodite, Dionysus, Apollo, Hecate, and Cybele. A series of steps, which were divided by a landing on which statues of the torchbearers stood, led down to the mithraeum. In some respects, this is similar to the typical placement of images of the torchbearers in other mithraea, at the start of the nave close to the entrance to the inner chamber. It is unusual for the torchbearers to appear outside the inner chamber, although this does echo the placement of the paintings flanking the entrance to the inner chamber at Hawarte, which possibly depict the torchbearers as riders.

Elsewhere in Rome there is the enigmatic structure located on the Aventine between the church of S. Saba and the Via Salvator. It consisted of a long corridor (ca. 20.00 × 2.95 m), to the western side of which were three niches, with the central niche smaller than the other two. The floors within the two larger niches were decorated with geometric patterns. A door opposite the most southernly niche opened into a structure of which only a few remnants survive but which evidently included a large rectangular basin (6.40 × 4.85 × 1.95 m deep). A column was situated on each corner of the basin, with a series of steps leading down into the basin on its south side. Architecturally there is nothing to indicate this space served a Mithraic function, but its use in the 4th c. as a location for Mithraic worship has been tentatively assumed on the basis of a small tauroctony found there.Footnote ⁴¹ The exact find spot of the relief was not recorded, however, and it appears very worn; thus, it may have only been deposited after it had ceased to be used as an item of worship.Footnote ⁴²

Nor were any benches found in the mithraeum at Lentia (Linz), which was constructed after 275 CE.Footnote ⁴³ The mithraeum was built from spolia erected on the remains of an earlier building, and its neighboring structures have been identified as temples to the Capitoline Triad and the Imperial Cult. It consisted of several rooms, with an inner chamber that was unusually small (5.10 × 2.70 m). The mithraeum contained two small circular tauroctony reliefs and an altar dedicated to Mithras. There was also a terracotta plate bearing a dedication to IOM and fragments of a votive offering that bears similarities to those found in temples to Jupiter Dolichenus. No evidence for any benches has survived. It has been suggested that they were made of wood and destroyed in the fire that seemingly marked the end of the mithraeum; however, the inner chamber was only 2.70 m wide, which if divided into a tripart bench-aisle-bench layout would leave only 0.9m for each section.Footnote ⁴⁴ Rarely are the width of benches in mithraea less than 1.5m, presumably to provide enough space for cult adherents to recline on; thus, the available space inside the inner chamber at Lentia makes the presence of two parallel benches unlikely.Footnote ⁴⁵ Indeed, of the mithraea discussed thus far, the interior chamber of the Lentia mithraeum is only larger than that of Via Giovanni Lanza. Moreover, the plan of the mithraeum depicts a burning deposit localized around where the cult image would have stood but not along the side walls. The mithraeum at Lentia is also unusual in that little evidence for meat consumption was found, but there was a notable quantity of fruit, nuts, and wheat in an adjoining room.Footnote ⁴⁶

Elsewhere, at Mackwiller in Germany there is evidence for a mithraeum that, at least in its final phases of use, had an appearance similar to that of a Romano-Celtic temple (Fig. 4). The foundations (ca. 10.00 × 8.19 m) of the building were constructed from ashlar blocks, inside which was a basin that was fed from a nearby spring.Footnote ⁴⁷ On the eastern side of the ashlar structure, the remains of a smaller structure with drystone foundations were also found. Various fragments of Mithraic sculptures were uncovered within the ashlar structure, the earliest of which were dated stylistically to the mid-2nd c. It was presumed by Jean-Jacques Hatt that the drystone building had been a shrine to the god of the spring, while the ashlar structure was part of a mithraeum. At the end of the 3rd c., the drystone structure was burnt down, while the ashlar structure, which also experienced fire damage, was refurbished and a drystone wall was erected around the central basin. The ashlar structure was later destroyed, in or just after 352 CE, at which time a ceramic vessel containing 404 coins was smashed on the floor, while other coins were found around an altar and the central water-basin. Various fragments from Mithraic sculptures were also deposited on the floor of the ashlar structure, many of them found against the wall opposite the entrance. A new building was then erected over the ashlar structure, which Hatt interpreted as a shrine to a spring deity. The terminus post quem for the destruction of the final building is the late 4th c.Footnote ⁴⁸

Fig. 4. Plan of the Mackwiller mithraeum. (D. Walsh after Hatt Reference Hatt1957, Fig. 3.)

Originally it was believed that the ashlar structure was the anteroom of a mithraeum as its form does not follow the established plan for an inner chamber, at least following the refurbishment conducted at the end of the 3rd c. However, there was no evidence for an adjoining room that contained two benches and a nave. Hatt hypothesized that the inner chamber was likely to have been dug into the rock of a nearby cliff face, although he acknowledged that if no such space was to be found (which to date it has not), then the square ashlar structure must be considered the inner chamber of a mithraeum.Footnote ⁴⁹ It also would have been unusual for so many fragments of Mithraic sculpture to have been deposited within an anteroom, as sculpture fragments recovered from mithraea tend to be found in the inner chamber. Moreover, the fragmentation of the sculptures and the deposition of their remains need not indicate the end of the use of a structure as a mithraeum. It is now evident that even in a fragmented state, Mithraic sculptures and ceramic vessels were still valued and retained by initiates. This has been demonstrated at Bornheim-Sechtem, where pieces of the same vessel were deposited in a shaft in the mithraeum at different times, while fire-damaged Mithraic sculpture fragments, seemingly retrieved from another mithraeum (there is no evidence for fire-damage to the Bornheim-Sechtem mithraeum), were stored in a niche.Footnote ⁵⁰ At Mainz, a ceramic vessel was ritually fragmented and deposited in the mithraeum, and similar evidence has been found at Tienen, Frankfurt, and Aquincum (Budapest).Footnote ⁵¹

The deposition of sculpture fragments also echoes how the remnants of Mithraic feasts might have been buried in and around mithraea. As Zena Kamash has suggested, “it may well be that breaking up the statues and burying them was a powerful act of forgetting to remember… In this way, the burial of the sculpture might be seen as a corollary of the deposits of chicken and pig bones buried in the floors.”Footnote ⁵² Evidence for the destruction of cult images by a cult's own adherents is not uncommon, particularly as part of a ritual of closure, as Philip Kiernan has observed. Structured depositions dating to the mid-2nd to mid-3rd c. at Le Bernard, for example, included fragments from various sculptures, while at Calès-Mézin two statues of Jupiter were buried outside a temple in the mid-2nd c., and at Kottenheim a hand from a cult statue was buried under the floor of the temple.Footnote ⁵³ Consequently, the evidence suggests that for at least the first half of the 4th c. the ashlar structure at Mackwiller hosted the worship of Mithras but appears closer in plan to a Romano-Celtic temple. Moreover, we cannot rule out the possibility that the smaller drystone structure also served a Mithraic function, possibly as an anteroom, given that there are no inscriptions or sculptures pertaining to the worship of a spring deity.Footnote ⁵⁴

At the London mithraeum, sometime in the early 4th c., the building experienced partial collapse.Footnote ⁵⁵ This may not have come as a surprise to the initiates, as it was not built on piles and was therefore susceptible to subsidence. The floor had already been re-laid several times in the half century since the mithraeum was built. As part of this restoration, the central aisle was raised to the same height as the benches, creating a level surface, and Mithraic sculpture fragments (alongside those from other deities such as Mercury, Serapis, and Minerva) were buried in the floor of the temple.Footnote ⁵⁶ Two altars were placed in front of the plinth on which the cult image had stood. It has been hypothesized these provided the base for a canopy under which a cult image sat. Wooden beams were also laid where the edges of the benches had once stood, suggesting that some form of tripartite division was maintained, albeit without the benches. This has been generally understood to mark the end of Mithraic activity in the structure, although the identity of the deity subsequently worshipped there has never been established conclusively. Bacchus has been suggested, given that a sculpture group consisting of the god with a retinue was found next to the north wall of the temple in the final floor phase. However, it has also been acknowledged that there is evidence to suggest a continued Mithraic use, including that the building contained an unusually high concentration of Camulodunum type 306 vessels both before and after the early-4th-c. structural alterations. The poor finish of these vessels may indicate they were intended for single use, most likely a particular ritual activity.Footnote ⁵⁷ Continued Mithraic use may also be indicated by the fact that the relative number of chicken bones also remains high after these structural alterations, while a (now lost) ceramic vessel containing chicken bones was found in a pit dug into the last floor layer of the building before its final abandonment.Footnote ⁵⁸

As discussed previously, it cannot be assumed that the fragmentation and deposition of Mithraic sculptures is indicative of these objects ceasing to be of importance to a Mithraic community. Moreover, it is possible that any Mithraic sculptures that were installed in mithraea during their last phases of use were removed upon the final destruction, as was the case with mithraea at Caernarvon, Colchester, Lambaesis, Lugo, and Orbe.Footnote ⁵⁹ In the case of London, several sculptures, including the small tauroctony dedicated by Ulpius Silvanus, were found in 1899. How they relate to the final phases of the mithraeum is unclear; it is possible that they were still on display in the temple.Footnote ⁶⁰ Incidentally, when the building finally went out of use sometime around the turn of the 5th c., several cattle skulls were deposited in the neighboring well, a strikingly coincidental act given the prominence of the bull in Mithraic iconography.Footnote ⁶¹ That being said, the continuation of Mithraic activity in the building does not mean that it was never utilized for the worship of Bacchus either, for the Bacchus statue group was discovered on the final floor layer, laid decades after the early-4th-c. alterations.Footnote ⁶²

Among these atypical mithraea it is also worth including the mithraeum at Septeuil near Paris, which was installed within a former nymphaeum in the mid-4th c.Footnote ⁶³ The mithraeum did contain two benches, but they did not align, with the bench to the left of the tauroctony considerably shorter (ca. 3.5 m) than that on the right (ca. 4.6 m) to allow for the doorway in the northeast corner of the chamber, which also meant it was situated further west than its counterpart. A statue from the former nymphaeum, depicting the goddess of the spring, was installed in a niche in the south wall above the longer bench. That the statue did not originally belong here is evident from the fact its feet had to be removed to fit it into the niche.Footnote ⁶⁴ Again, the mithraeum produced evidence for feasting, much of which related to the consumption of chicken.Footnote ⁶⁵

Finally, we may tentatively add a mithraeum constructed in 325 CE at Gimmeldingen in Germany. The structure is lost, but the inscription recording its precise date of construction refers to it as a fanum. Footnote ⁶⁶ This term has not been found in any other Mithraic inscription, for, as noted above, mithraea in Italy were generally referred to as spelaea (caves), while elsewhere they are usually called templa (temples).Footnote ⁶⁷ Fanum was a term often, although not exclusively, used to refer to Romano-Celtic temples, and its use here could suggest a structure in that style rather than a typical mithraeum. Incidentally, Mackwiller, with its mithraeum seemingly consisting of two concentric squares, lies only a day's travel from Gimmeldingen. Alongside the inscription, fragments of the tauroctony, reliefs depicting the torchbearers, a relief of Mercury, and another relief possibly depicting Vulcan and Minerva were recovered.Footnote ⁶⁸

Explaining the changes in Mithraic architecture

It should come as little surprise that a notable number of mithraea founded in the Late Roman Empire would break away from traditional bench-aisle-bench plan. Gordon argued that the founders of Mithraic communities were “inspired by a tradition… yet as leaders constantly on the look-out for new ideas and interpretations.”Footnote ⁶⁹ There is no reason as to why these varied influences would not eventually spread to the architectural arrangement of mithraea, particularly given that, as far as we can tell, there was no written Mithraic doctrine that decreed all mithraea had to maintain the same plan. It is possible that these new “ideas and interpretations” included the incorporation of deities and iconography from non-Mithraic traditions that we find in association with atypical mithraea: possibly Zoroastrianism or Manicheanism at Hawarte; Isis in the Mithraeum of the Colored Marbles; the lararium outside the Via Giovanni Lanza 128 mithraeum; spring deities at Mackwiller and Septeuil; Mercury, Vulcan (?), and Minerva at Gimmeldingen; and the sculptures of various deities deposited in the London mithraeum.Footnote ⁷⁰ There has been a tendency to focus on the Mithraic iconography as the subject of veneration while treating these other images as ancillary, yet it is plausible that these objects were also the subject of ritual activity. In some cases, this might be obscured in the archaeological record due to similarities between Mithraic rituals and rituals conducted in honor of other deities. The worship of Mercury, for example, evidently involved the sacrifice and consumption of chickens, while a raven frequently appears alongside both Mithras and Mercury.Footnote ⁷¹ That certain similarities between the gods led to them being worshipped simultaneously is evident from the various references to Mithras-Mercury in the epigraphic record.Footnote ⁷² However, there are aspects of these deities that are notably different, such as the consumption of ovicaprids in relation to the worship of Mercury and the initiation rites involved in the cult of Mithras. It might have been a desire to accommodate such differences that led the leaders of some Mithraic communities to design their mithraea with an “atypical” plan.Footnote ⁷³ Ritual practices and their architectural settings are deeply bound together, and a change to one, even relatively minor, can have a notable effect on the other. Several studies have drawn attention to this both in antique contexts and more generally.Footnote ⁷⁴

We should also consider whether for at least some later Mithraic adherents, the interior design of their mithraeum was not of primary importance. It is difficult to believe that every Mithraic initiate, even the leaders, understood how a mithraeum might serve as a map of the cosmos or knew the possible meanings encoded in the tauroctony. Even if they did, they might not have considered this a necessity. Indeed, the very variability in the design of mithraea in the Late Roman Empire illustrates this. For many Mithraic initiates, the mithraeum may have primarily served as a clubhouse in which they built social relationships with their contemporaries and superiors. This is not to suggest that this is mutually exclusive with a genuine belief in Mithras, but rather that this belief was not the main reason for their attendance at a mithraeum. As we have seen, evidence for feasting, the most communal of Mithraic activities, remains consistent into the Late Roman period regardless of whether the mithraeum had a traditional plan or not. For some it might simply have not mattered whether the mithraeum had two, one, or zero benches, nor where the image of tauroctony was situated, so long as they went home having had their share of the feast and having reaffirmed the bonds among themselves. As Kamash has observed, “sensual memory practices on religious sites and particularly those associated with Mithraism can be seen as a powerful way of linking diverse individuals who were not anchored by a shared sense of place or history.”Footnote ⁷⁵ Subsequently, such rituals developed and reinforced not only a sense of cult community, but also the community's attachment to the space in which they were performed. However, this did not necessarily mean that the space continued to be understood in quite the same way. Evidently in some cases there was a shift in how these spaces were perceived, as from the late 3rd c., mithraea started to appear that rejected the typical plan.

Wider socio-economic factors may also have played a role. It is perhaps no coincidence that atypical mithraea appeared at a time when the number of newly constructed mithraea (both standalone buildings and those installed in pre-existing spaces) entered into a decline (Figs. 5–6).Footnote ⁷⁶ This decline may have been due to an increasing rarity of able and/or willing patrons, as was already the case for temples more generally by this period.Footnote ⁷⁷ However, the number of mithraea installed in pre-existing structures/spaces does remain relatively more consistent into the 4th c. than their standalone counterparts (albeit with the number of those installed in pre-existing structures/spaces lower to begin with), which may have been due to the former being more economically viable. In any case, by choosing pre-existing spaces, these Mithraic communities were placing limitations on what could be achieved architecturally. At Septeuil, the design of the nymphaeum dictated that the benches had to be different lengths and unaligned. This might also be the reason why the Mithraeum of the Colored Marbles at Ostia contained just one bench, while at Lentia and Via Giovanni Lanza, the lack of benches might have been due to limited space within these rooms. That being said, the installation of several of these mithraea in caves (e.g., Epidaurum, Hawarte, and St Urban) might have resulted from a desire for a more “authentic” cave experience, rather than from financial restrictions. Indeed, meeting in an actual cave may have meant these adherents felt they could dispense with the typical mithraeum layout that was intended to replicate a cave.

Fig. 5. Construction of mithraea including Rome and Ostia. (D. Walsh.)

Fig. 6. Construction of mithraea excluding Rome and Ostia. (D. Walsh.)

In reality, there is no single explanation behind the emergence of atypical mithraea. Their very appearance is a testament to the variation that existed among Mithraic communities, each with its own aims and concerns. Some may have felt compelled to accommodate new forms of ritual practice, others may have been constrained by financial issues, and some may have felt it was enough to meet in an actual cave. Some of these factors are also not mutually exclusive, with the London mithraeum providing a possible example. The most probable explanation for the transformation of the inner chamber of this mithraeum in the early 4th c. is the initiates’ frustration at constantly having to re-lay the floor and repair the damage caused by subsidence. But why did they not continue to replicate the original plan, particularly as the installation of wooden beams where the benches had been suggests an attempt to at least respect the typical mithraeum layout? Perhaps the presence of sculptures depicting various deities in the mithraeum had already had an impact on ritual practices and the new layout reflected such changes. Yet even if this were the case, it does not explain why, given the major structural issues with the mithraeum, the initiates did not just move elsewhere. Was it, as has been suggested above, now too difficult to afford the construction of a new mithraeum? Or did the communal memories of ritual practices conducted within the temple mean the worshippers were too attached to the mithraeum to abandon it, even if it meant changes to the internal plan? It might be that all of these possibilities contributed to the changes in the internal appearance of the mithraeum. While we can trace some broader trends to help us hypothesize, it must be borne in mind that every temple had its own particular founder, community, and environment, all of which contributed to its unique biography.