Janus, the ancient Roman god of beginnings and transitions, gives January its name.
The month name January comes from the Latin Ianuarius, meaning the month of Janus. Roman tradition associated Janus with doorways, gates, passages, and changes because he was often depicted with two faces looking in opposite directions. This symbolism made him a natural figure for looking back at the old year and forward to the new one.
The Roman calendar's treatment of January changed over time. January 1 became the start of the consular year in 153 BCE, and the Julian calendar later helped establish the January-based arrangement that influenced the modern Gregorian calendar. The ancient Roman religious role of Janus is separate from the later Christian calendar traditions surrounding New Year's Day.
Janus is often confused with a generic symbol of the past and future, but he is a specific Roman deity. His name is also the source of words such as January, while the month itself is not named after the Roman god Jupiter.