During the Roman Saturnalia all class distinctions were abolished, with slaves and their masters switching roles, and laws that normally governed sensible behavior virtually suspended.
In medieval times, most Europeans adopted the Roman taste for a good time by electing a Lord of Misrule, or King of Fools. This harlequin king went by many names: King of the Bean in England, the Abbot of Unreason in Scotland, the Abbe de la Malgouveme in France. All had the power to call people to disorder. Cross dressing, bawdy songs, drinking to excess, and gambling on the church altar were only a few of the wanton acts reported.
In some places the Festival of the Ass was commemorated. A young girl with babe in arms entered a church riding an ass or donkey. During the mock services, prayer responses that would have normally included an 'amen' were substituted by a hearty 'hee-haw'.
Saturnalia took place from December 17 to December 23, with some variation in different periods of Roman history. There never was a standardized date for the medieval celebrations. Even Boxing Day carries a ghost of the old carnivals, or so I gathered from one of the later, lamer episodes of M*A*S*H. But as the Catholic Encyclopedia notes, the festivities tended to take place "on or about the feast of the Circumcision" -- that is, January 1. Its most famous American descendant, the Mummers Parade in Philadelphia, takes place on that same day, and so it is today that we'll mark it on this blog.
Scholars still debate whether the carnivals served as a safety valve, and thus ultimately undergirded the social hierarchy, or if they were something more revolutionary -- in Bakhtin's words, a liberatory "second world and a second life outside officialdom." The two positions are not mutually exclusive, and I doubt that there's a single answer to the question. I should note, though, that the Church eventually cracked down on the celebrations. Clearly, not everyone in the establishment felt that order was being reinforced.
I'll close with two quotes from James Frazer's The Golden Bough. One describes life during Saturnalia, when
masters actually changed places with their slaves and waited on them at table; and not till the serf had done eating and drinking was the board cleared and dinner set for his master. So far was this inversion of ranks carried, that each household became for a time a mimic republic in which the high offices of state were discharged by the slaves, who gave their orders and laid down the law as if they were indeed invested with all the dignity of the consulship, the praetorship, and the bench. Like the pale reflection of power thus accorded to bondsmen at the Saturnalia was the mock kingship for which freemen cast lots at the same season. The person on whom the lot fell enjoyed the title of king, and issued commands of a playful and ludicrous nature to his temporary subjects. One of them he might order to mix the wine, another to drink, another to sing, another to dance, another to speak in his own dispraise, another to carry a flute-girl on his back round the house.
The other recounts a rather forceful restoration of the ancien regime:
Roman soldiers at Durostorum in Lower Moesia celebrated the Saturnalia year by year in the following manner. Thirty days before the festival they chose by lot from amongst themselves a young and handsome man, who was then clothed in royal attire to resemble Saturn. Thus arrayed and attended by a multitude of soldiers he went about in public with full license to indulge his passions and to taste of every pleasure, however base and shameful. But if his reign was merry, it was short and ended tragically; for when the thirty days were up and the festival of Saturn had come, he cut his own throat on the altar of the god whom he personated.
And so the world is turned rightside-up again. Enjoy your holiday. You'll be back at work tomorrow.