As soon as the season allowed him to leave his winter quarters, Hannibal, determining as usual the course of the war and assuming the offensive, set out from Gerunium in a southerly direction, and marching past Luceria crossed the Aufidus and took the citadel of Cannae (between Canosa and Barletta) which commanded the plain of Canusium, and had hitherto served the Romans as their chief magazine.

The Roman army which, since Fabius had conformably to the constitution resigned his dictatorship in the middle of autumn, was now commanded by Gnaeus Servilius and Marcus Regulus, first as consuls then as proconsuls, had been unable to avert a loss which they could not but feel.

On military as well as on political grounds, it became more than ever necessary to arrest the progress of Hannibal by a pitched battle.
With definite orders to this effect from the senate, accordingly, the two new commanders-in-chief, Paullus and Varro, arrived in Apulia in the beginning of the summer of 538.

With the four new legions and a corresponding contingent of Italians which they brought up, the Roman army rose to 80,000 infantry, half burgesses, half allies, and 6000 cavalry, of whom one-third were burgesses and two-thirds allies; whereas Hannibal's army numbered 10,000 cavalry, but only about 40,000 infantry.

Hannibal wished nothing so much as a battle, not merely for the general reasons which we have explained above, but specially because the wide Apulian plain allowed him to develop the whole superiority of his cavalry, and because the providing supplies for his numerous army would soon, in spite of that excellent cavalry, be rendered very difficult by the proximity of an enemy twice as strong and resting on a chain of fortresses.