When day broke it seemed favourable to his design, for a thick mist was rising from the lake and marshes.

This, he thought, would conceal his advance from the Carthaginians, while, as the high ground ahead rose above the mist, he would be enabled to see their position.

He pushed forward then rapidly, thinking that he should be able to overtake the rear of the Carthaginian army as it moved slowly along encumbered with its plunder.
As he neared the entrance to the pass he caught sight of the heavy armed Carthaginians on the distant hill above the level of the mist, and believing that his own movements were hidden from the enemy, pushed forward as fast as the infantry could march.

But the moment the rear of his column had entered the narrow flat between the foot of the hills and the lake, the Numidians quietly moved down and closed the pass behind them, while Hannibal with his heavy infantry descended from the farther hill to confront him.

When all was ready he gave the signal, and at once in front, on their right flank, and on their rear the Carthaginians fell upon them.
The light troops heralded their attack by rolling a vast quantity of rocks down the hill on the long column, and then, pressing down through the woods, poured their arrows and javelins into the struggling mass.
Taken wholly by surprise, unable to advance or retreat, desperate at finding themselves thus caught in a trap, the Romans fought bravely but in vain.