As the god of beginnings, Janus also lent his name to the first month of the year. This month was referred to by the ancient Romans as Ianuarius - you can see how similar this word is to our own version (which is, of course, January).
The god Janus has a distinctive appearance in art, as he is often depicted with two faces. Some sources claim that the reason Janus was represented in this peculiar fashion was due to the notion that doors and gates look in two directions. In this way, one of the god's faces could look forward, while the other looked backward.
In addition, the Romans had an important temple to Janus, which was called the Ianus geminus. This temple served a symbolic function. When the gates of the structure were closed, this represented peace in the Roman Empire; but when the gates were open, it meant that the Romans were at war.
It worth noting that Janus was well respected and highly regarded by the ancient Romans. From his role as the guardian of gates and his position as the god of beginnings, to the honor of having the first month of the year named after him, it is clear that Janus played a significant part in Roman myth and religion.
Janus did not have a counterpart in Greek mythology.
Who's Who in Classical Mythology