The suffix "Primo" was added by the then king, Victor Emmanuel II of Italy, by a decree dated 10 December 1863 to distinguish Castano from another town of the same name in the Province of Pavia.
In 1863, King Victor Emmanuel II of Italy designated "Primo" as a distinguishing suffix for Castano, a town in the Province of Pavia, to differentiate it from another town with the same name.