Religion from Commodus to Theodosius I: ad 180–395
After the death of the “philosopher-king” Marcus Aurelius in ad 180, his son Commodus became emperor, and a period of political instability began. The dominant feature of the concluding period of Hellenistic influence—and shortly thereafter—was the rapid growth of Christianity throughout the Roman Empire, culminating in the conversion to Christianity of the emperor Constantine in 313 and the religious legislation of the emperor Theodosius affirming in 380 the dogmas of the Christian Council of Nicaea—which had been convened in 325 under the auspices of Constantine—and prohibiting paganism in a decree of 392. In this period the various Hellenistic cults were victims of active hostilities, which were expressed through prohibition, acts of violence, and theological polemics between “pagans” and Christians (e.g., the pagan philosophers Maximus of Tyre and Celsus, and the Christian philosophical theologians Irenaeus, Tertullian, and St. Clement of Alexandria, all of the 2nd century); but there were also brief periods of Hellenistic revitalization. The Neoplatonic school (based on a complicated system of levels of reality) of the 3rd-century philosophers Plotinus and Porphyry represented the culmination of Hellenistic religious philosophy. The Syrian solar cults of Sol Invictus (the “Unconquered Sun”) and Jupiter Dolichenus played an important role under the emperors Antoninus Pius, the Severans—Septimius, and Alexander—and Elagabalus and these were hailed as the supreme deities of Rome under Aurelian, whose Sun temple was dedicated in 274. From Parthia, the dualistic and spiritual teachings of the 2nd-century Iranian prophet Mani were widely disseminated throughout the Empire. The Persian cult of the ancient Iranian god of light, Mithra, spread rapidly throughout the western and northern Empire during the 3rd through 5th centuries. Although these various traditions enjoyed brief imperial patronage under Julian, they eventually were subsumed under the political and religious hegemony of Christianity (see below The influence of Hellenistic religions).