Janus, the two-faced Roman god, gives January its name and symbolizes looking backward and forward at New Year.
Roman tradition associated Janus with beginnings, transitions, gates and doorways. His two faces were commonly interpreted as facing in opposite directions, making him a natural symbol for the passage from an old year into a new one. January is named after him through the Latin month name Ianuarius.
Janus was especially connected with thresholds and changes rather than with one specific modern New Year's Eve ritual. Romans could invoke him at the start of undertakings, and January 1 became an important date in the Roman calendar and public life.
A frequent mistake is to identify Janus as a god of war because his name resembles January's position after December; the Roman war god was Mars. Janus is also not the source of the word “January” through Greek mythology: the name comes from Roman Latin.