Mithraism, also known as the Mithraic mysteries or the Cult of Mithras, was a Roman mystery religion centered on the god Mithras. Although inspired by Iranian worship of the Zoroastrian divinity (yazata) Mithra, the Roman Mithras was linked to a new and distinctive imagery, and the level of continuity between Persian and Greco-Roman practice remains debatable. The mysteries were popular among the Imperial Roman army from the 1st to the 4th century CE.

Mystery religions, mystery cults, sacred mysteries or simply mysteries, were religious schools of the Greco-Roman world for which participation was reserved to initiates (mystai). The main characterization of this religion is the secrecy associated with the particulars of the initiation and the ritual practice, which may not be revealed to outsiders. The most famous mysteries of Greco-Roman antiquity were the Eleusinian Mysteries, which predated the Greek Dark Ages. The mystery schools flourished in Late Antiquity; Emperor Julian, of the mid 4th century, is believed by some scholars to have been associated with various mystery cults—most notably the mithraists. Due to the secret nature of the school, and because the mystery religions of Late Antiquity were persecuted by the Christian Roman Empire from the 4th century, the details of these religious practices are derived from descriptions, imagery and cross-cultural studies. Much information on the Mysteries comes from Marcus Terentius Varro.