The battle of Lake Fucinus (89 BC) was a Roman defeat at the hands of the Marsians, which came after the Roman commander Lucius Porcius Cato was killed (Italian Social War).
Cato was one of the consuls for 89 BC, alongside Pompey Strabo. He was the uncle of Cato the Younger, a key figures in the Great Roman Civil War. At the start of the campaign of 89 Pompey was still engaged in the siege of Asculum in Picenum, while command of the war in the south went to Sulla. Cato was placed in command of the war against the Marsi, in the crucial areas to the east of Rome.
Cato doesn’t appear to have been a very lucky commander. A fragment of Cassius Dio records that most of his army was from Rome, and it was made up of over-age men who were unwilling to work hard or obey orders. When Cato attempted to regain control a mutiny broke out, and he was pelted with sods of earth. Only the lack of stones saved him from being stoned to death. The leader of the mutiny, give as Gaius Titius, was arrested and sent to Rome for trial, but avoided punishment.
Orosius gives us the longest account of this battle. Cato commanded an army that included the 'Marian forces', presumably those troops who had been commanded by Gaius Marius before ill health had forced him to retire. Marius's son, generally known as Marius the Younger, accompanied the army. Cato campaigned in the area to the east of Rome, where he won a number of otherwise unknown battles. This went to his head, and he boasted that even Marius hadn't accomplished greater deeds. Cato then advanced to Lake Fucinus (Facinus in Orosius), a large lake in the Apennines about fifty miles to the east of Rome (since then the lake has been drained producing an area of very fertile farm land). On the shores of the lake he clashed with the Marsi, who lived in the area around the lake. During the battle Marius the Younger killed Cato and made it look as if he had been killed by an unknown Marsian.
Livy and Appian also briefly mention the death of Cato. In Livy he won a series of victories over the Marsians, but was killed while storming one of their camps. Appian only records that he was killed fighting the Marsians during the winter, probably placing the battle early in 89 BC.
Livy is the only one of our sources that says how the battle ended, giving it as a Marsian victory.
Appian places the Marsian surrender in the winter of 89-88 BC, when Pompey Strabo, Cato's fellow consul for 89, forced their surrender, so this victory may have extended their resistance for most of 89 BC.