Janus, the ancient Roman god of beginnings and transitions, gave his name to January.
Romans associated Janus with doorways, gates, passages, and changes from one state to another. He was often depicted with two faces, one looking forward and one looking backward, making him a natural symbol for the transition from an old year to a new one. The Latin name for January, Ianuarius, derives from his name.
January became the first month of the Roman calendar in 153 BCE, when Roman consuls began taking office on January 1. The Julian calendar later retained that arrangement, and the Gregorian calendar used by most countries today also begins the year on January 1.
Janus is sometimes mistaken for a Greek god because many Roman deities have Greek counterparts. He has no exact Greek equivalent. His connection with beginnings explains why his name remains embedded in the modern word “January.”