Janus is one of the oldest gods of the Romans. Several myths exist about his origin, some stating that he as a mortal king of Latium, who ruled a city on a hill. The Tiber was his son.
He was the god of all beginnings and of passages such as doors, gates and bridges. When during sacrifices the first part of the offering was always to Janus, and he would always be named first in any list of gods.
The first month of the year, the beginning, was dedicated to Janus, and called January. His festival was celebrated in January 1st.
Janus was often depicted with two faces, and was then called Janus Bifrons.
There were several temples to Janus in Rome, the most famous was the one in the Forum Romanum, whose gates would be open in time of war, and only closed in times of peace.