Today, ante diem xvi kalendas januarias, is the 1st day of the ancient pagan Roman celebration of Saturnalia.
Saturnalia was a festival in honour of Saturn. There were banquets and people wore a soft floppy hat called a pileus.
No business could be conducted, so all the shops and markets were closed. People would gamble, eat a lot and exchange gifts. One custom was that masters would serve their slaves.