Sol Invictus Festival, Ancient Rome
This ancient holiday is the reason Christmas is celebrated on December 25th! Believers in Sol Invictus had the upper hand over Christianity during the reign of Emperor Aurelian (215-275). He made December 25th an empire-wide holiday representing the rebirth of the sun, a date later co-opted as the birth of Jesus Christ. Much like Saturnalia, the main guideline for celebrating the Sol Invictus Festival is to party your face off! Got to love the Romans. Pictured: a fresco depicting Sol Invictus.