Did Mithraism and other Roman cults surpass the original Greco-Roman religion in popularity before the rise of Christianity?

Question

From the death of Alexander the Great onward, the religion of the ancient Greeks steadily absorbed foreign elements creating new forms of worship and new deities. Some examples of newly worshipped deities include Serapis, Harpocrates , Mithras, Sol Invictus and so forth.

Also in this time, influential philosphical ideas started to spread such as Neoplatonism, Alatrism, Neopythagoreanism and others.

By the time of Emperor Constantine, was the worship of traditional Greco-Roman gods (Zeus, Athena, Heracles etc) by the general population as widespread as it was in pre-hellenistic times? Or had the beliefs in these old gods become out of fashion?

Answer 1

Yes Mithraism / Sun Worship was likely more popular than the Ancient Roman Pagan religions on the eve of Christianity's ascendancy. Constantine himself was said to be a sun worshiper, which is code for Mithraism.

Religious Facts
December 25 was also the birthday of the more popular Roman god known as the "Unconquered Sun" (with whom Constantine identified himself before his conversion to Christianity), who was closely associated with Mithras.

The sun god appeared on the flip side of Constantine's coins. The worship of Mithraism became synonymous with fidelity to the emperor.

Religious Facts:Mithraism
Archaeological finds indicate the extent of Mithraism included most of the Roman Empire, from Rome to Turkey to Britain. It was especially concentrated in Rome (35 Mithraic temples found) and its port of Ostia (15 temples).

The cult was supported by several emperors, including Commodus (180-92), Septimius Severus (193-211), and Caracalla (211-17). As part of an effort at renewing the Roman empire, Diocletian dedicated an altar to Mithra in Carnuntum (on the Danube near Vienna) in 307, designating the god patron of their empire (fautori imperii sui).

Most followers of Mithraism were Roman soldiers, minor government employees like customs officials, imperial freedmen or slaves. It was also adopted by the pagan aristocracy of 4th-century Rome, as part of a conservative movement in opposition to the new Christian empire based in Constantinople.