معرفت ادیان (Ma`rifat Adyan)

How the timing of initiation rites was determined remains an unresolved issue in the study of Roman Mithraism. This article asks whether the association of initiation grades with planetary deities, in addition to shaping Mithraic iconography and the symbolic organization of the cult, also influenced the selection of the days on which rituals were performed. The study focuses on the inscriptions of the Olympii family in Rome, which record several performances of the *Leontica*, the rites associated with the Lion grade, with precise dates. The research combines epigraphic criticism, historical analysis of religion, and astronomical reconstruction of the Moon’s position according to the Julian calendar. Since the Lions are placed under the protection of Jupiter in the evidence from Santa Prisca and Ostia, and Sagittarius and Pisces are the two domiciles of Jupiter in ancient astrology, the Moon’s position on the recorded dates was examined. On four clear dates out of the five principal dates, the Moon, at a fixed comparative time, was located in either Sagittarius or Pisces; the reconstructed date of 17 March 358 CE is also consistent with this pattern. Although one date does not fit the pattern, this convergence strengthens the possibility that certain Mithraic initiations were performed within “astronomically favorable windows” and opens a new avenue for investigating ritual time in Roman Mithraism.