Saturnalia was celebrated December 17th – 23rd.
Saturnalia was a lawless, drunken time in Rome where literally anything was okay. This was the original Purge, in which laws were suspended for a brief stretch of time. Saturn, the Roman god of agriculture, liberation and time, was celebrated at what is perhaps the most famous of the Roman festivals, the Saturnalia, It was a time of feasting, role reversals, free speech, gift-giving and revelry. (i.e.: gender-bending sex, drinking, telling people off, trading gifts and doing whatever you want).
After solstice, the darkest night of the year, the renewal of light and the coming of the new year was celebrated in the later Roman Empire at the Dies Natalis of Sol Invictus, the “Birthday of the Unconquerable Sun,” on December 25th.
Image: Saturnalia (1783) by Antoine Callet, showing his interpretation of what the Saturnalia might have looked like.