Mithraeum's a place of worship for the followers of the mystery religion of Mithraism. They were often constructed underground or in a cave to resemble the cave where Mithras's said to have slain the sacred bull (compare the very similar bull slaying depicted in the Enkidu seal). The word has come to be used in the context of any secret place used for secret rituals. Notable mithraea France Sarrebourg Germany Dieburg/Darmstadt Frankfurt-Heddernheim Freiburg im Breisgau, mithraeum relics… (More on Mithraeum)