The province was named for poeninus mons, the Roman name of the Great St Bernard Pass. Near the pass was a sanctuary dedicated to Jupiter Poeninus.
Because the name Poeninus is similar to Poenus (Latin for "Carthaginian"), some Roman authors inferred that the Carthaginian general Hannibal crossed this part of the Alps in his famous march on Italy in 218 BC, using either the Great St Bernard or Little St Bernard passes. The Roman historian Livy explains that Poeninus was actually a corruption of Penninus, the name of a deity worshipped by a local tribe. Livy adds that it was implausible that Hannibal took such a northerly route, as these high mountain passes would have been inaccessible at the time.