Final answer:
Roman mystery cults were characterized by secret initiation ceremonies, as seen in the cult of Mithras, and exhibited a hierarchical structure for initiates apart from the public worship and sacrifices of traditional Roman religion.
Step-by-step explanation:
An important feature of Roman mystery cults was their secret initiation ceremonies. These cults, devoted to the worship of a single deity, conducted esoteric rituals only known to and performed by initiated members. The Mithraic cult, for instance, which was particularly popular among Roman soldiers, held these initiation ceremonies in secret locations, such as caves, and they possibly had multiple levels of initiation, reflecting a hierarchical structure.
The mystery cults differed markedly from the public civic cults of Rome, which focused on customary practices and included activities such as mass animal sacrifices and a polytheistic worship approach. Notably, early Christians, also considered a mystery cult, abstained from traditional Roman cult practices like animal sacrifices and instead focused on prayer and communal worship without a secretive initiation process.