The Saturnalia was a large and important public festival in Rome. It involved the conventional sacrifices, a couch (lectisternium) set out in front of the temple of Saturn and the untying of the ropes that bound the statue of Saturn during the rest of the year. Besides the public rites there were a series of holidays and customs celebrated privately. The celebrations included a school holiday, the making and giving of small presents (saturnalia et sigillaricia) and a special market (sigillaria). Gambling was allowed for all, even slaves; although it was only officially condoned during this period, one should not assume that it was rare or much remarked upon during the rest of the year. It was a time to eat, drink, and be merry. The toga was not worn, but the pilleus (freedman's hat) was worn by everyone. Slaves were exempt from punishment, and treated their masters with disrespect. The slaves celebrated a banquet, before, with, or served by the masters. A Saturnalicius princeps was elected master of ceremonies for the proceedings. Saturnalia became one of the most popular Roman festivals which led to more tomfoolery, marked chiefly by having masters and slaves switch places, which led to widespread drinking and debauchery, so that among Christians the (lower case) word "saturnalia" came to mean "orgy".
The customary greeting for the occasion is a "Io, Saturnalia!" ? io (pronounced "yo") being a Latin interjection related to "ho" (as in "Ho, praise to Saturn").
