Saturnalia became one of the most popular Roman festivals. It was marked by tomfoolery and reversal of social roles, in which slaves and masters ostensibly switched places, much like the Lord of Misrule in later Christian celebrations.
Saturnalia was introduced around 217 BCE to raise citizen morale after a crushing military defeat at the hands of the Carthaginians.
Originally celebrated for a day, on December 17, its popularity saw it grow until it became a week-long extravaganza, ending on the 23rd. Efforts to shorten the celebration were unsuccessful. Augustus tried to reduce it to three days, and Caligula to five.
These attempts caused uproar and massive revolts among the Roman citizens.