LOUIS IL (825-875), Roman emperor, eldest son of the emperor Lothair I., was designated king of Italy in 839, and was crowned king at Rome by Pope Sergius II. on June 15, 844. In 85o he was crowned joint emperor at Rome by Pope Leo IV., and soon afterwards married his cousin, Engelberga, a daughter of King Louis the German, and undertook the independent govern-. ment of Italy. On the death of his father in Sept. 855 he became sole emperor. In 857 he allied himself with Louis the German against his brother Lothair, king of Lorraine, and King Charles the Bald, but after he had secured the election of Nicholas I. as pope in 858, he became reconciled with his brother. In 863, on the death of his brother Charles, Louis received the kingdom of Provence. In 864 he quarrelled with Pope Nicholas I. over his brother's divorce, which the pope had declared invalid, and in February reached Rome with an army, but made peace with the pope and left the city.
In 866 he routed the Saracens, but could not follow up his successes owing to the want of a fleet. In 869, with the assistance of his ally, the eastern emperor, Basil I., he captured Bari, the
headquarters of the Saracens. He had withdrawn into Benevento to prepare for a further campaign, when he was treacherously robbed and imprisoned by Adelchis, prince of Benevento, in Aug. 871, but was released a month later. Returning to Rome, he was crowned a second time as emperor by Pope Adrian II. on May 18, 872. After further successes against the Saracens, who were driven from Capua, he returned to northern Italy. He died, somewhere in the province of Brescia, on Aug. 12, 875, and was buried in the church of St. Ambrose at Milan, having named as his suc cessor in Italy his cousin Carloman, son of Louis the German.
See Annales Bertiniani, Chronica S. Benedicti Casinensis, both in the Monumenta Germaniae historica. Scriptores, Bande i. and iii. (Hanover and Berlin, 1826 fol.) ; E. Malbacher, Die Regesten des Kaiserreichs enter den Karolingern (Innsbruck, 1880 ; Th. Sickel, Acta regum et imperatorum Karolinorum, digesta et enarrata (Vienna, 1867-68) ; and E. Diimmler, Geschichte des ostfriinkischen Reiches (Leipzig, 1887-88).