Janus was the god of beginnings, gates, transitions, time, duality, doorways, passages and endings.
Residence: At the limits of Earth, at the extremity of the Heavens
Symbols: Two faces
Parents: Terra and Caelus
Siblings: Camese, Ops, Saturn
Consort: Camese
Children: Aithex, Canens, Fontus, Olistene, Tiberinus
Other Names: Ianuspater (Janus Father), Ianus Quadrifrons (Janus Fourfaced), Ianus Bifrons (Two-faced Janus)
He is usually depicted as having two faces, since he looks to the future and to the past. It is conventionally thought that the month of January is named for Janus.
Janus presided over the beginning and ending of conflict, and hence war and peace. The gates of a building in Rome named after him (not a temple, as it is often called, but an open enclosure with gates at each end) were opened in time of war, and closed to mark the arrival of peace (which did not happen very often). As a god of transitions, he had functions pertaining to birth and to journeys and exchange, and in his association with Portunus, a similar harbour and gateway god, he was concerned with travelling, trading and shipping.
Digital Maps of the Ancient World 