Although King Theudebald refused to send aid, he allowed two of his subjects, the Alemanni chieftains Leutharis and Butilinus, to cross into Italy.
According to the historian Agathias, the two brothers gathered a host of 75,000 Franks and Alemanni, and in early 553 crossed the Alps and took the town of Parma.
At Samnium they divided their forces, with Butilinus and the larger part of the army marching south towards Campania and the Strait of Messina.
The remainder managed to reach northern Italy and cross the Alps into Frankish territory, but not before losing more men to a plague, including Leutharis himself.
In summer, Butilinus marched back to Campania and erected camp on the banks of the Volturnus, covering its exposed sides with an earthen rampart, reinforced by his numerous supply wagons.
His army included infantry, heavy cavalry, and horse archers, and was thus at an advantage over the mostly infantry-based enemy forces.
As the Romans approached the Frankish camp, Narses sent an Armenian officer, Charananges, with a cavalry force to cut the Franks' supply.
They quickly penetrated the gap left by the Heruli, but Narses commanded his cavalry, which included many horse archers, to wheel on their flanks and attack the Franks from their exposed rear.