It was first mixed in Florence, Italy, in 1919, at Caffè Casoni (formerly Caffè Giacosa), located on Via de' Tornabuoni and currently called Caffè Roberto Cavalli. Camillo Negroni concocted it by asking barman to build it up.
1 1/2 ounces sweet vermouth
1 1/2 ounces gin
1 1/2 ounces Campari
Orange/twist for garnish
1Add all of the ingredients to an Old Fashioned glass and fill with ice.