Janus was a distinctively Roman god with no parallel in ancient Greek culture, acting as a supervisor to all things beginning and end. This included, but was not limited to, war and peace, passages, doorways and duality, hence his depiction as the man of two faces.

He was so closely related to the idea of change and the transition of times and states, that the Romans, in all of their creative naming might, decided to name the month of January in his honour. Quite the CV!