The highest number of mithraea in urban context of the ancient world come from Ostia. Although we do not know the whole city, mithraea have been found in all districts of the town. The spread and fortune of the Mithraic worship are also attested by the plenteous epigraphic and sculptural materials. This research deals with the Mithraism at Ostia, focusing on the particular case of monograms, just mentioned by Giovanni Becatti in his seminal work about mithraea at Ostia, dating back to more than sixty years ago. After the recent discovery of the Mithraeum of colored marbles by the archaeologists of the Ostia Marina Project (University of Bologna), it seems necessary to examine and contextualize the phenomenology of Mithraic monograms at Ostia, as is done in relation to similar processes which involve the Christian world.
In 2014, during the archaeological investigations carried out by the University of Bologna (Department of History and Cultures – Section of Archaeology), within the Ostia Marina Project, in the suburban neighborhood out of Porta Marina (block IV, ix), a new building has been found with outstanding Mithraic features. The building, for the special type of the marble floor of the spelaeum, has been conventionally called the “Mithraeum of colored marbles”. The spelaeum has a single bench, a ritual well and a flowerbed for a sacred plant. It differs clearly both in form and size from the typical patterns of the mithraea discovered until now in ancient Ostia. On the basis of the currently available data, a very late chronology (end of 4th century AD) can be proposed for the building.