Moreover, the pass of the Little St.Bernard, while not the lowest of all the natural passes of the Alps, is by far the easiest; although no artificial road was constructed there, an Austrian corps with artillery crossed the Alps by that route in 1815.
And lastly this route, which only leads over two mountain ridges, has been from the earliest times the great military route from the Celtic to the Italian territory.

The Carthaginian army had thus in fact no choice.

It was a fortunate coincidence, but not a motive influencing the decision of Hannibal, that the Celtic tribes allied with him in Italy inhabited the country up to the Little St.Bernard, while the route by Mont Genevre would have brought him at first into the territory of the Taurini, who were from ancient times at feud with the Insubres.
So the Carthaginian army marched in the first instance up the Rhone towards the valley of the upper Isere, not, as might be presumed, by the nearest route up the left bank of the lower Isere from Valence to Grenoble, but through the "island" of the Allobroges, the rich, and even then thickly peopled, low ground, which is enclosed on the north and west by the Rhone, on the south by the Isere, and on the east by the Alps.

The reason of this movement was, that the nearest route would have led them through an impracticable and poor mountain- country, while the "island" was level and extremely fertile, and was separated by but a single mountain-wall from the valley of the upper Isere.

The march along the Rhone into, and across, the "island" to the foot of the Alpine wall was accomplished in sixteen days: it presented little difficulty, and in the "island" itself Hannibal dexterously availed himself of a feud that had broken out between two chieftains of the Allobroges to attach to his interests one of the most important of the chiefs, who not only escorted the Carthaginians through the whole plain, but also supplied them with provisions, and furnished the soldiers with arms, clothing, and shoes.