Biography of Elagabalus
The height of Syrian influence was in the 3rd century AD when Sol, the Syrian sun god, was on the verge of becoming the chief god of the Roman Empire. He was introduced into Rome by the emperor Elagabalus (Heliogabalus) in about AD 220, and by about AD 240 Pythian Games (i.e., festivals of the sun god Apollo Helios) were instituted in many cities of the empire. The emperor Aurelian (270–275) elevated Sol to the highest rank among the gods. Sanctuaries of Sol and the gods of other planets (septizonium) were constructed. Even the emperor Constantine the Great, some 50 years later, wavered between Sol and Christ. For some time his religious policy was devised so as to allow the coexistence of both religions. Finally, Christianity was accepted as the official religion.
—Reinhold Merkelbach (2022) Mystery religion. Encyclopedia Britannica.