Although the final report of the results of the excavation at the Dura Mithraeum is not published yet, there are found many remarkable materials relating to the history of Mithraism in the Preliminary Report (1939). The art and the inscriptions as well as the circumstances of the dedications of this temple show that there was persisting influences of the religious and artistic "Koine", which established itself in the Semitic parts of the Parthian Empire during the first century B. C. On the other hand, the Dura Mithraeum was founded in one of the most critical period of the Durene history just after the occupation of the city by the Roman army in A. D. 165. So .the dedication must have not been against the will of the Roman military authority, and have followed the Roman usage of the Mithraic religion, which had been already planted on the soil of the Roman Empire by that time. From these observations an important problem arises whether its uniqueness, which seems to come from the "Koine", was merely a local peculiality of the whole system of Roman Mithraism or not. If not, it must represent some traits of pre-Roman Mithraism, which may have been the direct heir of the "Koine", and which did not follow the Roman usage of this mystery religion : it is possible that the first dedicators (the Palmyrene archers) had been initiated into the mystery earlier and brought it with its premitive tradition to Dura-Europos from Palmyra herself or from other parts of Syria before the Roman istion. Although we must wait for the publication of the final report to reach any solid conclusion, the examination of the archaeological data of the Preliminaly Report does not exclude the possibility that in Syria there was the pre-Roman Mithraic mystery, that is, the Mithraism of the period from the time of its founder to that of its Romanisation.