Janus

Roman religion gives Janus a standing that no other god shares: he is invoked at the start of every prayer and every religious rite, before Jupiter and before whichever god the rite is actually directed to, on the reasoning that no act can begin at all without first passing through Janus's domain of beginnings and openings. His name is bound up with ianua, the Latin word for door, and Roman households placed his image at the entrance to the home, facing both outward toward the street and inward toward the household at once, watching over who came and went in both directions simultaneously. City gates and the beginnings of roads and bridges carried his image or his protection for the same reason, and Roman religious calendars mark him as presiding specifically over transitions, the moment of stepping from one state, place or time into another, rather than over either side of the transition on its own.

Unlike most Roman gods, who have a fairly direct Greek counterpart absorbed into Roman practice, Janus has none, and Roman writers themselves treated him as a genuinely native Italian god rather than an import, one of the clearest cases of an authentically Roman rather than Hellenized deity at the center of the state religion.

The most politically visible expression of Janus's cult was a small shrine in the Roman Forum, the Ianus Geminus, built as a rectangular bronze structure with doors at both ends rather than a conventional temple, whose doors stood open whenever Rome was at war and were ceremonially closed on the rare occasions Rome was fully at peace with every neighbor at once. Roman historians treat closures as significant enough events to record individually precisely because they were so infrequent, noting only a handful across the many centuries of the Republic and early Empire, including one under Numa Pompilius traditionally credited as Rome's second king and religious founder, and a celebrated closure under Augustus that his own propaganda used as proof of the peace his rule had brought.

The doors standing open, by contrast, was simply the ordinary state of affairs for most of Roman history, a standing reminder that the city considered itself perpetually on a war footing even when no active campaign was underway. Janus also gives his name to the first month of the Roman calendar, January, understood from antiquity as the month that looks backward at the year just closed and forward at the one just opening, a double gaze that mirrors his two faced image and makes the New Year itself one more threshold under his particular protection.