He therefore told his colleague that although he saw the force of his arguments, public opinion in Rome was already so excited at Hannibal having been allowed, without a battle, to wrest so wide a territory from Rome, that it was absolutely necessary that an action should be fought.

The two armies were now united on the Trebia, and opinion was among the officers and troops, as between the consuls, widely divided as to the best course to be pursued.
Hannibal's spies among the natives kept him acquainted with what was going on in the Roman camp, and he determined to provoke the Romans to battle.

He therefore despatched two thousand infantry and a thousand cavalry to ravage the lands of some Gaulish allies of the Romans.
Sempronius sent off the greater part of his cavalry, with a thousand light infantry, to drive back the Carthaginians.
In the fight which ensued the Romans were worsted.

Still more furious, Sempronius marched to support them with his army.

Hannibal called in his troops and drew them off before Sempronius would arrive.