Janus is the Roman god associated with January, the month that begins the modern calendar year.
Janus was linked with doors, gates, beginnings, transitions, and endings. Roman tradition represented him with two faces, one looking forward and one backward, making him a fitting figure for the threshold between the old year and the new.
The Latin name Ianuarius became the English “January.” In the Roman calendar reforms associated with Julius Caesar, January 1 became the start of the civil year in 45 BCE, although calendar practices and political observance changed at different times.
Janus is not the same deity as Saturn, whose festival Saturnalia influenced some Roman seasonal customs but was held in December. Nor is January named for a Roman emperor; its name comes from the god's Latin name.