Pantheon: Roman, Latin
Janus is the god of beginnings and endings, and doorways. His festival was held on January 17th. The Romans named January, the first month of the year, after Janus, and dedicated January 1st to him. The doors to his temple in the Forum in Rome were only closed during times of peace. He is the first god named when praying, and the first god to recieve a sacrifice.
In art Janus is seen as having two faces: one facing forwards and one facing backwards.
Janus Bifrons: "Janus with Two Faces"