Janus was an ancient Italian god. The distinctive mark of Roman religion and Roman gods as opposed to Greek gods is that the former are abstract, while Greek thought was marked by its anthropomorphism. In the belief of the Roman everything and every action had its corresponding spirit – even such processes as plowing, harrowing, etc. Janus tried by this test, approves himself as peculiarly Italian. He is "the spirit of opening," and there is nothing in the mythology of any other Aryan nation to correspond to him. His name is derived from the same root as the Latin word janua, "a gate" or "an opening." As the spirit of opening he was invoked at the beginning of all undertakings (at the beginning of human life as Consivius). For the same reason he was the god of the beginning of day, Matutinus Pater, and of the beginning of the (agricultural) year, the first month of which, January (though originally the eleventh of the calendar year), was dedicated to him. Hence, too, may be explained the fact that he took precedence of all other gods, even of Jupiter, and that he is called in the Saliaric Hymn Deorum Deus (Macrob. Sat. i. 9), and even Summanus.


In the next place, as the spirit of openings, Janus was the god under whose care were all januae, or gates, in Rome; above all, he it was under whose protection was the arch-way out of which the army marched to war and by which it returned. This arch-way, which in later times, was replaced by a temple of Janus, naturally had its gates open in time of war and closed in time of peace. The tutelary god of the gate that opened both ways was, by a natural transference of thought, himself represented as an image having a double head that looked both ways.


His connection with the year was sometimes indicated by the fact that three fingers of the right hand were bent so as to indicate the numeral CCC (300), while the fingers of the left hand were spread so as to denote the numerals L (50) + V (15), or in later times L + V + V + V – that is, in all, the 355 days of the older, and the 365 days of the reformed Julian year. As the god of the gates he naturally carries keys. As an auspicious god he is crowned with laurel.