God of Every Threshold

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.