The temple of Janus with closed doors, on a sestertius issued under Nero in 66 AD from the mint at Lugdunum

Janus was a two-faced god of Roman mythology who kept the gate of Heaven. He was the god of beginnings and ends, and so of gates, doors, doorways and passages. 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 (Ianuarius) in his honor. In January we look back on the last year and forward to the next.