The first major obstacle that Hannibal army faced was the crossing of the Rhone River. The Rhone River was a wide and fast-flowing river, and the Carthaginians did not have any boats. Hannibal's solution was to build a bridge across the river. He used a variety of materials, including tree trunks, animal skins, and ropes, to construct the bridge. The bridge was completed in five days and the army was able to cross the river.