The origin of the cult of Mithras in the Roman Empire has been the object of considerable enquiry. The circumstances in which Mithraism met its last end have aroused less interest, though the evidence for the finaldays of Mithraism could shed light on larger questions concerning the ending of non-Christian cult in the Roman Empire. Paganism was brought to an end by many means. Laws made by emperors played a part; their primary target, from the time of Constantine onwards, was traditional public sacrifice (Bradbury 1994; Turcan 1984: 209-19). So did bishops and gangs of monks, men 'who eat more than elephants' in the complaint of an unsympathetic observer, who delighted to dismember pagan temples, and could assemble substantial mobs to help them (Libanius Oration 30: 8; Fowden 1978). Less coercive causes for the end of pagan cult are not so easy to discern; some temples, for instance, must simply have succumbed to the fire risk endemic to ancient cities (cf. Pliny Letter 10: 33, with Sherwin-White 1966: 606-8). Understanding will come only when we have a comprehensive study of the fate of pagan cult-sites. (Deichmann (1939) is anything but comprehensive. There is considerable matter in Trombley (1993-4), though the assumption that taurobolium was a Mithraic ritual (I: 340; II: 26) does not inspire confidence.) In the meantime a brisk consideration of the evidence from Mithraea raises some questions.
Temples of Mithras are of interest not because Mithraism posed a particular threat to the success of Christianity, but because the temples form a body of evidence that is well-defined and widely dispersed. The remains of Mithraea are known from as far afield as Hadrian's Wall in Britain and the foothills of the Atlas mountains in Algeria. The internal layout of these temples is singularly uniform. If they were not actually underground, they were made to look as though they were - artificial crags around the entrance were sometimes added to give the sanctuary the appearance of a cave, as at one temple at Carnuntum on the Danube frontier (CIMRM 1664). The fact that so many Mithraea were constructed underground ought to be a benefit to those who might wish to date their abandonment. It makes them less likely than conventional temples to have been re-used for other purposes, or robbed of their stone by enterprising epigonoi. The excavator of one gloomy vault under Rome found it undisturbed since it had been left in Late Antiquity: 'il complesso rimasce intatto fino al momento della sua venuta in lace durante lo scavo' (Lissi-Caronna 1986: 47). The fortunate investigator may find direct evidence of the manner in which a temple of Mithras was abandoned and the date at which this occurred.
Two obstacles have prevented the assembly of a full dossier of these circumstances. One is the character of the operations in which some Mithraic sanctuaries were originally uncovered, the other is a tendency on the part of those who have studied them to assume that the last condition of Mithraea was always the product of violent action by Christian opponents of the cult. The first obstacle is easily described, though not so easily overcome. Many Mithraea were first uncovered in the last century and the excavators - in their enthusiasm to ascertain the appearance of the temples when they were in use - often destroyed or failed to record evidence about the conditions of their abandonment. The famous Mithraeum under the apse of the church of San Clemente in Rome may be taken as one of many. The wall which sealed its entrance might, says a recent writer, have provided valuable indications about the date when the Christians invaded the building to provide an apse for their church, but unfortunately the evidence was destroyed in the excavations of 1869-70 (Guidobaldi 1978: 249). A thorough perusal of the Corpus Inscriptionum et Monumentorum Religionis Mithriacae (CIMRM) reveals relatively few temples where the recorded evidence of their condition suggests the manner of their end. …