Janus, the ancient Roman god of doorways and transitions, gave January its name and became associated with New Year beginnings.
Janus was traditionally depicted with two faces, one looking forward and one looking backward. This imagery connected him with thresholds, departures, arrivals, and the transition from one state to another. The Latin name for January, Ianuarius, derives from his name.
The Roman calendar’s arrangement changed over time, but January 1 became the start of the civil year in the Julian calendar introduced by Julius Caesar in 46 BCE. Janus was especially appropriate for the date because the beginning of a year looks back on the past and forward to what is coming.
Janus is often confused with Saturn because Saturn was another major Roman deity and the focus of Saturnalia. Saturnalia was a December festival, whereas Janus is the deity most directly linked with January and transitions.