The Roman columns advanced without hesitation into the unoccupied pass; the thick morning mist concealed from them the position of the enemy.
As the head of the Roman line approached the hill, Hannibal gave the signal for battle; the cavalry, advancing behind the heights, closed the entrance of the pass, and at the same time the mist rolling away revealed the Phoenician arms everywhere along the crests on the right and left.

There was no battle; it was a mere rout.

Those that remained outside of the defile were driven by the cavalry into the lake.

The main body was annihilated in the pass itself almost without resistance, and most of them, including the consul himself, were cut down in the order of march.

The head of the Roman column, formed of 6000 infantry, cut their way through the infantry of the enemy, and proved once more the irresistible might of the legions; but, cut off from the rest of the army and without knowledge of its fate, they marched on at random, were surrounded on the following day, on a hill which they had occupied, by a corps of Carthaginian cavalry, and--as the capitulation, which promised them a free retreat, was rejected by Hannibal--were all treated as prisoners of war.