Which pass did Hannibal cross with elephants?

The Alps, in 218 BC, and which pass specifically has been argued over for two thousand years - Polybius and Livy disagree, and modern candidates include the Col de la Traversette, the Col du Clapier and several others. A 2016 paper claimed evidence from a churned-up layer of soil at the Traversette containing horse-gut microbes, which is either the answer or a very muddy field.

He had 37 elephants and most of them died. The crossing itself cost him perhaps half his army to cold, ambush by local tribes and the terrain, and he arrived in Italy with around 20,000 infantry from a force several times that size. The elephants were largely gone within a year; the point of the manoeuvre was that nobody expected an army from the north at all.

He then spent fifteen years in Italy without losing a battle and without winning the war. Cannae in 216 destroyed a Roman army of perhaps 80,000 in a double envelopment still taught in staff colleges, and Rome simply refused to negotiate, raised more men, avoided pitched battle, and eventually attacked Carthage to force him home. He was beaten at Zama in 202 by a Roman general who had studied his methods, and the Carthaginian cavalry that had won him Cannae was on the other side.