A cavalry skirmish followed, in which he was wounded and rescued by his son, a lad of seventeen, afterwards the famous Africanus.

The Romans were discomfited, with considerable loss.
They then retreated, crossing the Po at Placentia, and destroying the bridge behind them.

Hannibal forded the river farther up, and marched along its right bank until he reached its confluence with the Trebia, opposite Placentia.

Here he encamped.
Meanwhile Sempronius, who had been recalled from Sicily, relieved the disabled Scipio.
Early one raw morning in December, 218, the vanguard of the Carthaginians was ordered to cross the Trebia, and, as soon any resistance was met, to retreat.

The other troops of Hannibal were drawn up ready to give the enemy a hot reception, if, as he expected, they should pursue his retreating vanguard.