Janus is the Roman god who gives January its name and is linked with looking backward and forward at the New Year.
Roman tradition associated Janus with beginnings, transitions, doorways, gates, and passages. He was commonly represented with two faces, one looking toward the past and the other toward the future. This imagery made him a natural symbol for the change from one year to the next.
The Latin name for January is Ianuarius, derived from Janus. In the Roman calendar reform traditionally associated with King Numa Pompilius, January became the first month, although the calendar's structure and the official start of the administrative year changed at different points in Roman history.
Janus should not be confused with Saturn, whose festival Saturnalia occurred in December, or with the Greek god Hermes, who corresponds broadly to the Roman Mercury. The English word “January” preserves Janus's name, while New Year's Eve customs themselves vary widely across cultures and do not all descend from Roman practice.