Cold and hungry, the Roman army obeyed, and the Punic cavalry retreated across the river before the enemy.
The Roman foot soldiers were ordered to follow, although the water was cold as ice, and reached almost to their shoulders. When they scrambled up on the other bank, they were chilled to the bone as well as faint for want of food. More miserable bedraggled Roman soldiers had never been seen. They were scarcely fit to attack a small body of the enemy, much less to face the main body of the Carthaginian army, which, well fed and warm, awaited them in battle array.
Hannibal, with his usual care for his soldiers, had seen that they had a good meal, after which he had bade them rub their bodies with oil in front of the camp fires, before they buckled on their armour.
It was soon plain that the Romans were not fit to cope with the comfortable Carthaginian troops.
Yet in spite of the elephants, that trampled them underfoot, and in spite, too, of the Punic cavalry which was stronger than their own, the Roman legions held their ground.
It was only when the signal had been given, and Mago, with two thousand men rushed from his ambush, and attacked them in the rear, that the Romans gave way.
Then they turned and fled towards the Trebia, hoping to be able to cross it and to regain their camp. But many of them were cut down before they reached the river, while, of those who attempted to recross the cold and swollen waters, many were drowned.
Only ten thousand in the centre of the Roman army succeeded in keeping their ranks unbroken. These brave soldiers pushed their way through the enemy and retreated to Placentia, a town on the river Po, which had already been taken and fortified by their own legions.
Before the day was over the Carthaginians, too, had suffered severely from the weather. Showers of rain and snow forced them at length to give up the pursuit of the Romans and hasten to their tents for shelter and warmth. Many of the elephants perished in the storm.
When Rome heard of the defeat of her two armies, and that both her Consuls were shut up in Placentia with a remnant of their soldiers, she was dismayed at the greatness of the disaster. Moreover, she was well aware that this victory would make the Gauls cleave more steadfastly than before to the successful general.