The united consular armies, he represented, should take up their position on the river Trebia.
This river rose in the Apennines but a short distance from Genoa, and flowed nearly due north into the Po at Piacenza.

The Roman army there would therefore effectually bar Hannibal's march into the rich plains to the east, and would prevent him from making across the Apennines and following the road by the coast, as they would, should he undertake such a movement, be able to fall on his rear.
Hannibal pitched his camp on the Nure, about five miles from Piacenza, but Scipio remained immovable in his lines waiting for the arrival of his colleague.

Hannibal's position was a difficult one.

He had traversed the Pyrenees and the Alps that he might attack Rome; but between him and Southern Italy lay yet another barrier, the Apennines.

Scipio had missed him after he had crossed the Pyrenees, had been too late to attack him when, exhausted and worn out, his army emerged from the Alps; but now, united with Sempronius, he hoped to crush him at the foot of the Apennines.