The Battle of Mons Lactarius (also known as Battle of the Vesuvius) took place in October 552 AD during the Gothic War (535–554) between Byzantine forces and the Ostrogoths (Goths) near Mount Vesuvius in Italy.
After the defeat and death of the Gothic King Totila at the Battle of Taginae, the Goths chose Teias as their new king, who attempted to gather allies and the remaining Gothic forces. The Byzantines, led by Chamberlain Narses, moved to besiege Cumae, where much of Totila's war chest resided. Upon this news, Teas moved to break the siege, but Narses intercepted him in the rugged terrain near Mount Vesuvius. After two months of stalemate, the two sides engaged in open battle. Teias was killed in the fighting, marking the collapse of Gothic leadership. The remaining Gothic troops resisted for a short time but ultimately surrendered under negotiated terms. This victory ended the Gothic state, allowing the Byzantines to reestablish their authority in the Italian Peninsula.
Background
In 540, the capital of the Gothic kingdom, Ravenna, was surrendered to general Belisarius, effectively bringing most of the Italian Peninsula under Byzantine control. However, after his recall to Constantinople, the corruption by the Byzantine commanders and the harsh taxation of the Italian populace reignited the Gothic resistance.
The new Gothic king, Totila, reorganized the Gothic forces and gained support by treating Italian civilians more fairly than some Byzantine officials had. Totila successfully recaptured much of Italy, including important cities and territories that had previously been lost. In response, the Byzantine emperor Justinian I sent the Chamberlain Narses to lead a new campaign against the Goths. At Salona in the Dalmatia region, a Byzantine army had been assembled under the supervision of John the Sanguinary, comprising regular Byzantine units and several contingents of foreign allies, notably Lombards, Heruls, and Gepids. Narses marched around the Adriatic Sea and through Italy to reach Rome. Totila was compelled to intercept Narses before reaching Rome. The two armies engaged in combat near Taginae, where Totila was mortally wounded, and much of his Gothic army was defeated and scattered.
Prelude
thumb|right|upright=1.1|Map of the [[Bay of Naples]]
After the death of Totila, the remaining Gothic forces gathered to Ticinum, where they chose the former second-in-command, Teias, as their new king. Teias sent envoys to the Franks in hopes of forming an alliance against the Byzantines, but the Franks refused, preferring to let the Goths and Byzantines wear each other down, thereby easing their eventual conquest of Italy.
Narses marched towards Rome, seizing in the process the towns of Narni and Spoleto. Rome was recaptured without difficulty in July 552, and the keys of its gates were delivered to Justinian. When the Goths learned that Rome had fallen, they executed their hostages, including senators along with their families and 300 children whom Totila had taken from the leading families of various cities. They also carried out widespread killings against the Italian population, spreading fear and violence throughout the region. After the fall of Rome, Narses continued to besiege Cumae. Upon this news, Teias marched to break the siege because Totila's hoard was stored in Cumae and was necessary to fund the war. In response, Narses moved his army to block Teias near Mount Vesuvius.
Battle
thumb|right|upright=1.1|Battle on the slopes of the [[Mount Vesuvius. Depiction by Alexander Zick, 1890]]
Upon arrival, Teias positioned himself at the foot of Mount Vesuvius, near the site of Pompeii, on the left bank of the Sarno. The Byzantines and Goths stood across a small stream for two months, with only minor skirmishes between them and single combat at the only bridge over the stream. The Goths had camped near the bridge of the stream and erected towers with ballistas. However, the Byzantines cut off the Goths' supplies, forcing Teias to take action before his army faced starvation.
The Goths withdrew from their initial position towards Mount Lactarius, where they lured the Byzantine army into rough terrain. At this location, they launched a surprise attack that took place on 1 or 30 October, with the Byzantines holding their ground. Both armies dismounted, due to the terrain, and adopted a deep phalanx formation. Teias led his forces in an attack on the Byzantine lines, but the Goths could not break through. The Byzantine troops attempted several times to kill Teias with throwing spears, only for Teias's comrades to resupply him with new shields. After several attempts, Teias died in the fight. Teias's head was taken by the Byzantine soldiers and fixed on a stake to discourage the Goths from fighting. The Gothic troops continued to fight for another two days. In the end, they sent an envoy to negotiate permission to withdraw from Italy while keeping their own money for travel expenses. John advised Narses to accept the proposal, warning of the risks of a prolonged battle against the Goths' fierce resistance. Narses agreed to terms under strict conditions.
Aftermath
thumb|right|upright=1.2|The Byzantine Empire after the end of the Gothic War in 555
The Gothic survivors were released under the oath to leave Italy, taking with them only their personal money and movable property, deposited in various fortresses in Italy as traveling funds. The battle marked the end of the Ostrogoths in the Italian Peninsula. A thousand Goths under the leadership of Indulf broke away from the agreement and resisted along with other Goth leaders, Aligern (Teias's brother) in Cumae and Ragnaris in Conza della Campania. The Goths failed to appoint a new king, which exposed the fragility of their remaining power. Narses quickly captured a number of cities that lacked Goth garrisons, including Florence, Centumcellae, Volaterrae, and Pisa.
The defeat of the Goths triggered another request from the Goths north of the River Po to the Franks to intervene.
A 75,000-strong Frankish army, under Alamannic dukes Lothar and Buccelin, moved south to Italy in the following year. While the Franks outnumbered the Byzantines, the Byzantines had better supplies and fortifications. In October 554, Narses defeated the Franks in the Battle of the Volturnus, eliminating them as a threat. The remaining cities in Italy under the Goths started to fall, notable cities were Campsa in 555 and Verona in 561.