Janus coin from Republican Rome, c. 225-12 BCE.                           Image courtesy of VROMA.org

Janus was one of the earliest gods, worshipped before Rome was founded as a city. He was the god of beginnings, and endings, and is often represented in two-headed form, looking both forward and backward. He was associated with doorways, gates and archways, and was the first god invoked in any sacrifice. The first month of the year was named after him, January. There was a cult in his honor on a hill in Rome, which was named after him, the Janiculum.