January is named after Janus, the Roman god associated with beginnings and transitions.
Janus was commonly represented with two faces, one looking forward and one looking backward. That image made him a fitting figure for the start of a new year, when people reflect on the past and anticipate what is ahead. The Latin name for the month was Ianuarius.
January became the first month of the Roman calendar in the second century BCE, after calendar reforms associated with the Roman king Numa Pompilius and later adjustments by Roman authorities. The Roman calendar's structure changed over time, so the month did not always occupy the same position in every early system.
The month is directly relevant to New Year's celebrations because January 1 became the civil New Year's Day in the Julian calendar and remained so in the Gregorian calendar. The name is sometimes incorrectly linked to the Roman god Jupiter, but Janus is the deity specifically connected with doors, passages, and new beginnings.