|The Roman god Saturn|
The day was a public holiday and even schools were closed. Gifts were exchanged and everyone was supposed to have fun. Everyone wore their best clothes and togas - a symbol of rank - were forbidden. Instead everybody wore the 'freedman' hat.
A Saturnalian prince was chosen from among the youngest members of the family and he ruled over the rest for the day.
The correct greeting was 'Io, Saturnalia!' (Meaning Ho - praise to Saturn.) It was pronounced Yo.
So... Yo! Saturnalia to you all.