Totila, aware of the looming threat, was determined to deny his enemies their last important bases on Italian soil, most prominently Croton and Ancona. He withdrew from Sicily, and while his troops besieged Ancona, with 47 ships blockading it from the sea, he sent the rest of his fleet, 300 ships strong, to raid the coast of Epirus and the Ionian Islands. Ancona was likely to fall soon, and therefore the Roman general Valerian, commander of Ravenna, called upon John, a very experienced general who was stationed at Salona in Dalmatia awaiting the arrival of Narses and his army, to send a relief force. John immediately manned 38 ships with his veterans, and was soon joined by 12 more ships under Valerian himself. The joint fleet set sail for Sena Gallica, some north of Ancona.
Unlike in classical Antiquity, the warships of the 6th century did not feature rams; naval combat was therefore dominated by missile exchanges and boarding actions. In this form of combat, experience and the ability to maintain a formation of ships was essential, and the Byzantine crews held the advantage over the inexperienced Goths. Soon, in the heat of battle, some Gothic ships drifted off the main body and were easily destroyed, while others sailed too close together and were unable to maneuver. In the end, the weary Gothic fleet disintegrated and their ships fled as best as they could. They lost 36 ships, and Gibal was captured, while Indulf with the remainder fled towards Ancona. As soon as he came close to the Gothic army's camp, he beached his ships and set them on fire.
This staggering defeat disheartened the Gothic force, which immediately abandoned the siege and withdrew. Followed soon after by a series of Roman successes, the battle of Sena Gallica can truly be regarded as marking the beginning of the turn of the tide of the Gothic War in the Empire's favour.