Janus, the Roman god of beginnings and transitions, gives January its name.
The Latin name for January is Ianuarius, derived from Janus. Roman tradition portrayed Janus with two faces, allowing him to look toward the past and the future. That imagery made him especially suitable for a month associated with a boundary between years, although the historical calendar’s New Year customs changed over time.
January 1 became the opening of the Roman consular year in 153 BCE, when newly elected consuls began their terms on that date. The Julian calendar later retained January as the first month, and the Gregorian calendar continues the convention used by most of the world today.
Janus should not be confused with Saturn, whose festival Saturnalia was held in December, or Mars, who gave his name to March. The modern New Year’s holiday combines calendar history with later religious and civic traditions.