Saturnalia

 was a popular Roman holiday dedicated to the god Saturn. It included sacrifice, and many people gave small statuettes of Saturn to their friends. The ceremony culminated with the unbinding of the feet of a giant statue of Saturn. During this holiday, masters and slaves traded positions for the day, with the slaves being equal to their masters. A theory existed that 25 December was chosen for the date of Christmas because Saturnalia already existed on that date.

In the 1st century BC, the Seventh Doctor and Ace visited Rome during Saturnalia. During this time, the god Saturn awoke and took control of the slaves, trying to incite them to rebellion. Saturn's wife, Rhea, with the help of the Doctor and Ace, defeated him. (PROSE: The Best of Days)