The disappointment and rage of the Roman general were great, and Hannibal felt that he could now bring on a battle when he would.

He determined to fight in the plain close to his own position.

This was flat and bare, and was traversed by the Trebiola.

This stream ran between steep banks below the level of the plain; its banks were covered with thick bushes and reeds, and the narrow gap across the plain was scarce noticeable.
On the evening of the twenty-fifth of December Hannibal moved his army out from the camp and formed up on the plain facing the Trebia, ordering the corps commanded by his brother Mago to enter the bed of the Trebiola, and to conceal themselves there until they received his orders to attack.

The position Mago occupied would bring him on the left rear of an army which had crossed the Trebia, and was advancing to attack the position taken up by Hannibal.