Magnus Decentius (died 18 August 353) was caesar of the Western Roman Empire from 350 to 353, under his brother Magnentius.

History

Nothing is known of Decentius prior to 350. Magnentius usurped power from Constans on 18 January 350, and elevated Decentius as caesar later that year, perhaps in July or August. He was appointed consul in 352. In the following year, after he had lost the battle of Mursa Major, Magnentius' exactions to finance the war drove Gaul into revolt against his dictatorial rule, and Decentius was expelled from the capital, Treves, which headed the revolt. The Alamanni began to invade the province, perhaps at the instigation of the emperor Constantius II in order to increase pressure on the usurper. Decentius, who led his brother's forces in the north, was defeated in a pitched battle by the Alemannic chief Chnodomar, and besieged in Sens. There news reached him of Constantius' victory at the Battle of Mons Seleucus, and the subsequent suicide of Magnentius. Decentius hung himself, signalling the end of the civil war.

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