Janus, the ancient Roman god of beginnings and transitions, gave January its name.
The Roman month Ianuarius was named for Janus, whose name is also preserved in the English word “January.” Janus was associated with doorways, gates, passages, and changes from one state to another. Because New Year's Day marks a transition between years, the god became especially relevant to year-end and year-beginning symbolism.
Janus is commonly represented with two faces looking in opposite directions. This imagery is often interpreted as looking toward the past and the future, making it a natural symbol for reflection at New Year's Eve. The two-faced image does not mean the god was simply a deity of deception; his central role concerned thresholds and transitions.
The Roman calendar changed over time, and January was not always the first month in the earliest Roman system. January and February were later placed at the beginning of the calendar, helping establish the arrangement that influenced the modern Gregorian calendar.