Battle of Forum Julii

After assuming the imperial throne during the civil war, Otho campaigned to secure the passes in the Alps bordering Gaul, as well as those territories whose loyalties toward him were in doubt. As a part of these campaigns, he sent his fleet to secure Gallia Narbonensis, which had sworn allegiance to Vitellius, Otho's primary opposition, and potential (and later successful) usurper of the throne.

According to Tacitus (Histories 2.14), Fabius Valens, after hearing of the threat to Gallia Narbonensis, responded as follows:

He despatched two cohorts of Tungrian infantry, four squadrons of horse, and all the cavalry of the Treviri under the command of Julius Classicus. Part of these troops were retained for the defence of the colony of Forum Julii, for it was feared, that if the whole [Vitellianist] army were sent by the route through the interior, the [Othonian] fleet might make a rapid movement on the unprotected coast. Twelve squadrons of cavalry and some picked infantry advanced against [Otho's forces]; they [the Vitellianists] were reinforced by a cohort of Ligurians, an auxiliary local force of long standing, and five hundred Pannonians, not yet regularly enrolled.

The battle began as soon as the armies met. A rash attack on behalf of the Vitellian auxiliaries led to them being surrounded:

The conflict commenced without delay, the enemy's line of battle being so arranged, that part of the levies from the fleet, who had a number of rustics among their ranks, were posted on the slope of the hills which border on the coast, the Prætorians fully occupying the level ground between the hills and the shore, while on the sea was the fleet, moored to the land and ready for action, drawn up in line so as to present a formidable front. The Vitellianists whose infantry was inferior, but who were strong in cavalry, stationed the mountaineers on the neighbouring heights, and their infantry in close ranks behind the cavalry. The squadrons of the Treveri charged the enemy incautiously, and found themselves encountered in front by the veteran troops, while on the flanks they were also annoyed by showers of stones from the rustic band, who were skilful throwers, and who, mixed up as they were among the regular soldiers, whether cowardly or brave, were all equally bold in the moment of victory. The general consternation of the Vitellianists was increased by a new alarm as the fleet attacked the rear of the combatants. By this movement they were hemmed in on all sides, and the whole force would have perished, had not the shades of night checked the advance of the victorious army, and covered the retreat of the vanquished.

Despite the loss, the Vitellianist forces, specifically the fierce Tungrian auxiliaries, retaliated against their enemy, who had relaxed in the joy of victory (Histories 2.15):

The Vitellianists, however, though beaten, did not remain inactive. They brought up reinforcements and attacked the enemy, who felt themselves secure, and whose vigilance was relaxed by success. The sentinels were cut down, the camp stormed, and the panic reached the ships, till, as the alarm gradually subsided, they again assumed the offensive under the protection of some neighbouring heights which they had occupied. A terrible slaughter ensued, and the prefects of the Tungrian cohorts, after having long maintained their line unbroken, fell beneath a shower of missiles. The Othonianists, however, did not achieve a bloodless victory, as the enemy's cavalry wheeled round, and cut off some who had imprudently prolonged the pursuit.

The Vitellianists retreated to Antipolis, a town of Gallia Narbonensis, the Othonianists to Albigaunum, in Upper Liguria, who subsequently blockaded the province from unfriendly forces.

When Fabius Valens heard of the loss, he sent a detachment of Batavian auxiliaries to the relief of the province. Tacitus makes a note of this action (Histories 2.28) with an anecdote on the well-known strength of the Batavians, and the subsequent risings of a mutiny on behalf of the Vitellianist legions. Due to the feeling of fear/loss that the legions had when these brave compatriots of theirs were sent away for the aforementioned mission, Valens was forced to deal with said brief mutiny of his troops.