Janus is the Roman god who gives his name to January, the month that begins the Gregorian calendar year.
Janus was associated with beginnings, transitions, doorways, gates, and passages. Roman artistic tradition commonly portrayed him with two faces, one looking forward and one backward. That imagery made him a fitting symbol for the boundary between the old year and the new one.
The Latin month name Ianuarius developed from Janus's name. January was not always the first month in every Roman calendar. Early Roman traditions placed March at the beginning of the year, but January became the opening month of the republican calendar by the second century BCE, partly because Roman consuls began their terms on January 1.
The modern Gregorian calendar retains January 1 as New Year's Day. Its name therefore preserves a direct link between an ancient Roman deity and a date now marked by fireworks, parties, resolutions, and midnight countdowns around the world.