To their surprise, Hannibal found another way across that continues to impress us. He may have tricked the elephants into believing the raft they were about to float on was still on dry land. It's also possible he used the elephants' herding instinct to his advantage.
Here's a passage from the Augustan era Roman historian Livy's history of Rome from its founding (Ab urbe condita), XXI.28, on Hannibal's crossing the Rhône with his elephants:
"In the transport of the elephants I believe different plans were adopted; at all events, the accounts of what took place vary considerably. Some say that after they had all been collected on the bank the worst-tempered beast amongst them was teased by his driver, and when he ran away from it into the water the elephant followed him and drew the whole herd after it, and as they got out of their depth they were carried by the current to the opposite bank. The more general account, however, is that they were transported on rafts; as this method would have appeared the safest beforehand so it is most probable that it was the one adopted. They pushed out into the river a raft 200 feet long and 50 feet broad, and to prevent it from being carried down-stream, one end was secured by several stout hawsers to the bank. It was covered with earth like a bridge in order that the animals, taking it for solid ground, would not be afraid to venture on it. A second raft, of the same breadth but only 100 feet long and capable of crossing the river, was made fast to the former. The elephants led by the females were driven along the fixed raft, as if along a road, until they came on to the smaller one. As soon as they were safely on this it was cast off and towed by light boats to the other side of the river. When the first lot were landed others were brought over in the same way. They showed no fear whilst they were being driven along the fixed raft; their fright began when they were being carried into mid-channel on the other raft which had been cast loose. They crowded together, those on the outside backing away from the water, and showed considerable alarm until their very fears at the sight of the water made them quiet. Some in their excitement fell overboard and threw their drivers, but their mere weight kept them steady, and as they felt their way into shallow water they succeeded in getting safely to land."


