The name of Trivigliano is probably explained by the Latin tres vigilantes: three who keep watch, that is the three towers of the walled circuit, which also appear on the coat of arms granted by decree of the President of the Republic on 31 July 1997 (others would refer it instead to a Roman family that owned an estate here). Of those three towers, on the walls, one is left: a round keep, the only survivor of the watch and defence towers that once stood there. The village, in short, goes on counting three in its name and showing three on its shield, while it has just one still standing.
The number three comes back, and this time with visible consequences. Trivigliano lies in the Ernici mountains, between 538 and 781 metres, among woods of turkey oak and chestnut, and within its territory is Lake Canterno, which has a date of birth: 1821. It is a karst lake born of a blockage — the plain had three swallow holes that drank the water of the heavy rains, two of them gradually clogged up, and the water, no longer finding its way underground, stayed where it was. Today the lake is a nature reserve. The village, for its part, has been devoted from the beginning to Saint Oliva, whose church keeps an old effigy of her, and the feast falls on 11 June.