In Roman mythology, Janus (or Ianus) was the god of gates, doors, doorways, beginnings and endings. His most prominent remnants in modern culture are his namesakes: the month of January, which begins the new year, and the janitor, who is a caretaker of doors and halls.
Janus was usually depicted with two heads looking in opposite directions. According to a legend, he had received from the God Saturn, in reward for the hospitality received, the gift to see both future and past.
In general, Janus was the patron of concrete and abstract beginnings, such the religion and the Gods themselves, of the world and the human life, of new historical ages, economical enterprises. He was also the God of the home entrance (ianua), gates, bridges and covered and arcaded passages (iani).
He was frequently used to symbolize change and transitions such as the progression of past to future, of one condition to another, of one vision to another, the growing up of young people, and of one universe to another. He was also known as the figure representing time because he could see into the past with one face and into the future with the other.
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Roman bust of Janus, Vatican Museums.