Janus appears to have been a uniquely Roman god, perhaps originating as a local deity before his establishment in Rome. It is though he was introduced to the city by Romulus himself.
According to tradition Janus is known as the "god of two faces," and the god of beginnings; therefore he presided over gates and doorways. Also he is the god of the past, present and future.
He is depicted as having two faces looking in opposite directions, which symbolizes his dominance over the past and future. He holds a key in his right hand and a staff in the left when invoked as the guardian of gates, doorways, and roadways; alternatively he holds the numbers 300 and 65 when presiding over the beginning of a new year. Also, he was equated the rising and setting sun. Each new season, and the dawn of each day were sacred to him. He was particularly worshipped at New Year, and January is derived from his name. The Janus Quadritons temple was reputedly a perfectly symmetrical square, each side possessing one door representing the four seasons, and three windows collectively comprising the twelve months of the year.
The Janus geminus, his gateway to the northeast of the Roma forum, was shut in times of peace (only four times prior to the Christian era) and open in times of war. A.G.H.
Grimal, Pierre, Larousse World Mythology, Secaucus, New Jersey, Chartwell Books, 1965, p. 178
Jordan, Michael, Encyclopedia of Gods, New York, Facts On File, Inc. 1993, p. 124