Secret rituals of pagan religions, known only to select initiates who had qualified for higher spiritual development. Such mysteries were kept apart from popular worship, and initiates had to take a binding oath of secrecy, so that even today our knowledge of the mysteries is partly conjectural. Typical mystery cults were those of Eleusis in Greece from about 1500
B.C.E., in turn deriving from the mystery religions of ancient Egypt and the mysteries of Mithras, a Persian deity. Traces of Mithraism existed in Britain. Many secret societies in modern times have claimed that their rituals are a descent of an ancient tradition.
Sources:
Ulansey, David. The Origins of the Mithraic Mysteries: Cosmology and Salvation in the Ancient World. New York: Oxford University Press, 1989.
