Since the year 240 BC the asses and other Roman bronze coins depicted the double-faced god Janus and a prora, the prow of a galley, most likely a quinquereme.
Janus was the god of gates and doorways, of entrance and exits, of beginnings and ends. He was the name giver for the month of January, the month that looks back upon the old year and ahead into the new. Janus was the one, moreover, who according to Roman mythology tought men the use of money as well as navigation.
The prora, the prow of large Roman ships, was a symbol for the entire boat. Their depiction on Roman coins is interpreted as a reference to Roman naval power.