Janus, the ancient Roman god who looked toward both the past and the future, gave January its name.
Janus was associated with beginnings, transitions, doorways, gates, and passages. Roman artists commonly represented him with two faces, allowing him to look in opposite directions. That image later became a symbol of reflection on the year ending and anticipation of the year beginning.
The Latin month name Ianuarius was derived from Janus. January became the first month of the Roman calendar in 153 BCE, when Roman consuls began taking office on January 1. Earlier Roman calendars had used March as the beginning of the year, so the position of January changed over time.
Roman New Year customs included honoring Janus and making offerings, while later cultures developed their own midnight rituals. Janus is often mistakenly described as a god of time itself; his more precise associations are thresholds and transitions. The two-faced image also explains why modern writing uses “Janus-faced” for something with contrasting aspects.