When Hannibal was planning to march on Rome, he sent scouts out ahead of time to find the best routes through the mountains.
He wanted to go through before winter sent in and they would become unpassable. He left Spain in the Spring of 218 B.C., but
did not make it to the Alps until late fall and encountered some harsh conditions, costing him dearly in terms of men and
elephants. He also had to deal with the local tribes, who would throw down rocks and boulders down the narrow pass at the
troops. He lost many men and elephants to falling off the sides of the mountains. He eventually made it out but his numbers
were cut in half. He would eventually make up those troops with the addition of the Gauls.