How did the Alps help the Roman empire?

The Alps in the northern part of the Italian peninsula provided a natural barrier to invaders. The Alps, however, were not insurmountable and incursion by barbaric tribes were part of early and late Roman history. Also, as formidable as these mountains were, the Carthage general Hannibal was able to cross the Alps with a large army and war elephants during the 2nd Punic War.