Roman emperor, was the eldest son of the emperor Louis I., and his wife Irmengarde. Little is
known of his early life, which was probably passed at the court of his grandfather Charlemagne, until 815 when he became ruler of Bavaria. When Louis in 817 divided the Empire between his sons, Lothair was crowned joint emperor at Aix-la-Chapelle and given a certain superiority over his brothers. In 821 he
married Irmengarde (d. 851), daughter of Hugo, count of Tours; in 822 undertook the government of Italy; and, on the 5th of April 823, was crowned emperor by Pope Paschal I. at Rome. In November 824 he promulgated a statute concerning the relations of pope and emperor which reserved the supreme
power to the secular potentate, and he afterwards issued various ordinances for the good government of Italy. On his return to his father’s court his step-mother Judith won his consent to her plan for securing a kingdom for her son Charles, a scheme which was carried out in 829. Lothair, however, soon changed his attitude, and spent the succeeding decade in constant strife over the division of the Empire with his father. He was alternetely master of the Empire, and banished and confined to Italy; at one time taking up arms in alliance with his brothers and at another fighting against them; whilst the bounds of his appointed kingdom were in turn extended and reduced. When Louis was dying in 840, he sent the imperial insignia to Lothair,who, disregarding the various partitions, claimed the whole
of the Empire. Negotiations with his brother Louis and his half-brother Charles, both of whom armed to resist this claim, were followed by an alliance of the younger brothers against Lothair. A decisive battle was fought at Fontenoy on the 25th of ]une 841, when, in spite of his personal gallantry, Lothair
was defeated and fled to Aix. With fresh troops he entered upon a war of plunder, but the forces of his brothers were too strong for him, and taking with him such treasure as he could collect, he abandoned to them his capital. Efforts to make peace were begun, and in ]une 842 the brothers met on an island in the Sâone, and agreed to an arrangement which developed, after much difficulty and delay, into the treaty of
Verdun signed in August 843. By this Lothair received Italy and the imperial title, together with a stretch of land between the North and Mediterranean Seas lying along the valleys of the Rhine and the Rhone. He soon abandoned Italy to his eldest son, Louis, and remained in his new kingdom, engaged in alternate quarrels and reconciliations with his brothers, and in futile efforts to defend his lands from the attacks of the Normans and the Saracens. In 855 he became seriously ill,and despairing of recovery renounced the throne, divided his lands between his three sons, and on the 23rd of September entered the monastery of Priim, where he died six days later. He was buried at Prüm, where his remains were found in 1860. Lothair was entirely untrustworthy and quite unable to maintain either the unity or the dignity of the empire of Charlemagne.
See "Annales Fuldenses"; Nithard, "Historiarum Libri," both in the Monumenta Germaniae historica. Scriptores, Bände i. and ii. (Hanover and Berlin, 1826 fol.); E. Mühlbacher, Die Regesten des Kaiserreichs unter den Karolingern (Innsbruck, 1881); E. Dümmler, Geschichte des ostfränkischen Reichs (Leipzig, 1887-1888); B. Simson, Jahrbücher des deutschen Reiches unter Ludwig dem Frommen (Leipzig,1874-1876).