Volunteers were summoned to arm, and those legally exempt from military service were included in the levy.
Nevertheless, they were taken by surprise.

Far earlier than either friends or foes expected, Hasdrubal was on the Italian side of the Alps (547); the Gauls, now accustomed to such transits, were readily bribed to open their passes, and furnished what the army required.
If the Romans had any intention of occupying the outlets of the Alpine passes, they were again too late; already they heard that Hasdrubal was on the Po, that he was calling the Gauls to arms as successfully as his brother had formerly done, that Placentia was invested.

With all haste the consul Marcus Livius proceeded to the northern army; and it was high time that he should appear.

Etruria and Umbria were in sullen ferment; volunteers from them reinforced the Phoenician army.
His colleague Gaius Nero summoned the praetor Gaius Hostilius Tubulus from Venusia to join him, and hastened with an army of 40,000 men to intercept the march of Hannibal to the north.

The latter collected all his forces in the Bruttian territory, and, advancing along the great road leading from Rhegium to Apulia, encountered the consul at Grumentum.