Final answer:
The Mysteries of Isis and the Mithraic Mysteries were the two most popular foreign cults in ancient Rome, each offering esoteric rituals, sacred artifacts, and a hierarchical system of initiation. The Mithraic Mysteries were noted for their popularity among Roman soldiers, while both suffered a decline with the rise of Christianity as the state religion.
Step-by-step explanation:
The two most popular foreign cults in ancient Rome were the Mysteries of Isis and the Mithraic Mysteries, which appealed to many outside traditional Roman religious practices. The Mysteries of Isis derived from Egypt and incorporated Egyptian artifacts and motifs within their sanctuaries, such as obelisks and hieroglyphs. In contrast, the cult devoted to the god Mithras, originating from ancient Persia, demonstrated a more subtle approach to its Persian heritage with few overtly Persian elements visible in its rites and imagery.
The appeal of these cults could be compared to that of modern forms of Buddhism in the West, which find more success when they align with Western Enlightenment values, such as reason and tolerance. Both cults developed hierarchical initiation rituals that were secret and offered membership ranks to their followers. The Mithraic Mysteries, in particular, became well-received among the Roman military due to their principles of brotherhood and loyalty, which resonated well with the soldiers' own values.
The rise of Christianity later led to the decline of these and other mystery religions in Rome, as Christianity eventually became the official state religion, under Emperor Constantine, in 380 CE.