A Mithraeum is a place of worship for the followers of the mystery religion of Mithraism. The Mithraeum was either an adapted natural cave or cavern or an artificial building imitating a cavern. Mithraea were dark and windowless, even if they were not actually in a subterranean space or in a natural cave. When possible, the mithraeum was constructed within or below an existing building. The site of a mithraeum may also be identified by its separate entrance or vestibule, its "cave", called the… (More on Mithraeum)