signposts placed at a three way road junction

Dunno about signposts. Way I heard it there were shrines to Diana at places where three roads came together and that Diana was worshipped under the name Trivia. Origin of tivia meaning worthless information may come from the lesser of the two divisions of the seven liberal arts in medieval universities. The divisions were the trivium and the quadrivium. The trivium were grammar, rhetoric and logic. The quadrivium were umm, geometry, astronomy, arithmetic and music. I had to look it up; never can remember them'ns. Quadrivium, that is. Trivium I remember.