await his colleague Sempronius, who had been recalled from Sicily, when it became known that Hannibal meant to invade Italy.
Although the fight at Ticinus was only a skirmish, yet the victory of Hannibal's cavalry encouraged many Gallic tribes to throw off their fear of Rome and join the Carthaginians.
Even those Gauls who had joined the Roman camp were eager to escape, and one night more than two thousand of them mutinied, and, overpowering the sentinels, left the Romans to join Hannibal.
After the flight of the Gauls, Scipio thought it would be wise to move to a safer position, so he marched to the upper Trebia, another tributary of the Po. Here he was joined by Sempronius.
Hannibal was eager to fight while the Gauls were still faithful to him, for he, as well as the Romans, knew their unstable character. Scipio on the other hand, wished to delay meeting the enemy, for he was still wounded. Moreover, he thought that if a battle did not take place soon, the Gauls would be more than likely to forsake their new ally.
But Sempronius, who had entire charge of both the Roman armies since Scipio was wounded, could brook no delay.
The Carthaginian general had already discovered that it would be easy to tempt the second Consul to fight. He therefore determined to entice him to cross the river Trebia.
It was winter. Heavy rains and sleet had fallen, and the river was flooded, when, early one bleak morning, Hannibal ordered his brave young brother Mago, with a large number of troops, to lie in ambush in a dried-up watercourse, where they were hidden by high banks and tall bushes. Until a signal bade them dash out upon the enemy, they were not to stir.
Meanwhile a body of Carthaginian cavalry had been
