Janus is the God of beginnings and transitions, hence also of gates, doors, passages, endings and time. He is usually depicted as having two faces, since he looks to the future and to the past. The Romans named the month of January in his honor.

Janus presided over the beginning and ending of conflict, and hence war and peace. The doors of his temple were open in time of war, and closed to mark the 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.

The ancientGreeeks had no equivalent to Janus, whom the Romans claimed as distinctively their own. Modern scholars, however, have identified analogous figures in the pantheons of the Near East. His name in Greek is 'Ιανός (Ianós).