Sol Invictus
The Romans held a festival on December 25 called Dies Natalis Solis Invicti, "the birthday of the unconquered sun." The use of the title Sol Invictus allowed several solar deities to be worshipped together, including Elah-Gabal, a Syrian sun god; Sol, the patron god of Emperor Aurelian (AD 270-274); and Mithras, a soldiers' god of Persian origin. Emperor Elagabalus (218-222) introduced the festival, and it reached the height of its popularity under Aurelian, who promoted it as an empire-wide holiday that was a possible inspiration of Christmas.