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.