Rise of Byzantium: Battle of the Volturnus

The Battle of the Volturnus, also known as the Battle of Casilinum or Battle of Capua, was fought in 554 between an army of the Eastern Roman Empire and a combined force of Franks and Alemanni. The Byzantines, led by the old eunuch general Narses, were victorious.
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. A bridge over the river was fortified by a wooden tower, heavily garrisoned by the Franks.
When Narses found out about the location of the Frankish camp, he set forth at the head of an 18,000 strong force, including strong contingents of Heruli mercenaries. His army included infantry, heavy cavalry, and horse archers, and was thus at an advantage over the mostly infantry-based enemy forces.
At the pleas of the Heruli general, Sindual, who promised to persuade his men to fight, he left a gap in the middle of the infantry, which the Heruli were to occupy.
However, two Heruli had deserted to the Franks, and persuaded Butilinus to attack now while the Heruli stayed out of the battle. The Franks arrayed in a large wedge formation and advanced, and smashed into the Byzantine centre. 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. The Franks, already engaged with the Byzantine infantry, were unable to turn and face their more mobile enemies in the rear. As confusion started to spread amongst them, the Heruli finally returned to the fray. In the words of J.B. Bury, "... then Sindual and his Heruli appeared upon the scene. The defeat of the Franks was already certain; it was now to be annihilation."
Butilinus and most of his men perished, while Roman casualties were small. Agathias gives the impossibly low number of 80 Byzantine casualties, while claiming that only five Goths survived. Whatever the true numbers, it was a magnificent victory for Narses, and signaled the final triumph of the Byzantine Empire in Italy. Despite Narses' great victories, the war was not finished. Seven thousand Goths held out at Campsa, near Naples until they capitulated in the spring of 555. The lands and cities across the River Po were still held by Franks and Goths, and it was not until 562 that their last strongholds, the cities of Verona and Brixia, were subjugated.