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. A mithraeum was a place of worship for the followers of Mithraism, often constructed in a cave to resemble the cave where Mithras is said to have slain a sacred bull. The word has come to be used to refer to any secret place used for rituals. This one dates back to Etruscan times, and began as a tomb, before being adapted by followers of Mithras in Roman times. In the Middle Ages it was converted to a church.
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This measures 40 m x 50 m and is excavated out of the tuff rock. It is believed to be Roman, from the 1st century AD. The layout suggests that spectators stood, rather than sat, while watching proceedings. It seems to be rarely open to the public, but the amphitheatre is clearly visible through the gate.