Janus
In ancient Roman religion and myth, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces. The month of January is named for Janus. According to ancient Roman farmers' almanacs, Juno was mistaken as the tutelary deity of the month of January; but, Juno is the tutelary deity of the month of June. Janus presided over the beginning and ending of conflict, and hence war and peace. The gates of a building in Rome named after him were opened in time of war, and closed to mark the arrival of peace. As a god of transitions, he had functions pertaining to birth and to journeys and exchange, and in his association with Portunus, a similar harbor and gateway god, he was concerned with travelling, trading and shipping. Janus had no flamen or specialised priest assigned to him, but the King of the Sacred Rites himself carried out his ceremonies.
