Janus is the ancient Roman god whose name gives January its name and whose symbolism is linked with New Year.
Janus was associated with beginnings, transitions, doorways, gates, and passages. Roman artistic representations often show him with two faces, one looking forward and one looking backward, making him a natural symbol for the transition from one year to the next.
The month January, or Ianuarius in Latin, was named for Janus. The Roman calendar's organization changed over time, but January eventually became the first month of the Julian and later Gregorian calendar traditions used widely today.
Janus is not the Roman god of time itself; that role is often mistakenly assigned to him in modern explanations. His central idea is transition and the opening of a new phase.