Louis II, d. 875, emperor of the West (855–75), king of Italy (844–75), son of Emperor of the West Lothair I. In 844, Lothair I designated him king of Italy and in 850 he was crowned emperor of the West in Rome. He became sole emperor when his father died; the title had little meaning, however, since he ruled only in Italy. Throughout his reign, his power there was challenged by the independent Lombard dukes and by the Arab invaders of S Italy. In the dispute between his brother Lothair, king of Lotharingia, and Pope Nicholas I, concerning Lothair's divorce, he supported his brother. However, the pope refused to allow Lothair to set aside his wife even after Louis occupied Rome (864). Subsequently, Louis submitted to the pope's decision. At Lothair's death (870) Louis claimed Lotharingia, but the Treaty of Mersen divided it between his two uncles, Charles the Bald (who succeeded Louis as Emperor of the West Charles II) and Louis the German.