Janus, the two-faced Roman god, gave January its name and became linked with New Year beginnings.
Janus was associated with doors, gates, transitions, and passages. His two faces were traditionally understood as looking in opposite directions, making him a fitting symbol for looking back at the old year and forward to the new one. The Latin name for January is Ianuarius, derived from Janus.
The Roman calendar's treatment of January changed over time. January and February were added to the calendar tradition later attributed to the Roman king Numa Pompilius, and January became the first month of the republican Roman calendar in 153 BCE. This helped align the start of the civil year with the beginning of new consular terms.
Janus is not the same figure as Saturn, whose festival Saturnalia was held in December. Modern New Year's celebrations use Janus symbolically, even though Roman religious practice and today's countdown traditions are very different.