LOTHAIR I, Emperor, King of Italy. — Eldest son of Louis the Pious and Queen Ermengarde, born about 785, died at Prüm on 28 September 855. In July 817 his father Louis conferred upon him at Aachen the title of Emperor and in 822 entrusted him with the Kingdom of Italy. After the Assembly of Attigny, he came to Rome and on 5 April 823 was crowned Emperor by Paschal I. The following year he returned to Rome to quell the disturbances that had broken out and with the *Roman Constitution* regulated the relations between Papacy and Empire and established norms for the election of the pope. Then at Corteolona (May 825) he enacted the capitularies relating to the administration of the Italian Kingdom, ecclesiastical discipline, and the organization of schools.
to quell the disturbances that had broken out and with the *Roman Constitution* regulated the relations between Papacy and Empire and established norms for the election of the pope. Then at Corteolona (May 825) he enacted the capitularies relating to the administration of the Italian Kingdom, ecclesiastical discipline, and the organization of schools.
When Louis the Pious (Worms, August 829) sought to alter the division of the Empire in order to favor his youngest son Charles the Bald, Lothair rose in revolt with his brothers against their father, forcing him to annul the new division (Compiègne, May 830). At the new Assembly of Nijmegen (831), having secured confirmation of his possession of Italy, he returned there; but as the divisions in Francia were renewed, his strongest supporters wished to uphold the Constitution of 817 as an effective guarantee of the unity of the Empire and the peace of the Christian world. Lothair crossed the Alps again, together with Pope Gregory IV, and at Rothfeld he joined his brothers in humiliating their father at the Assembly of Compiègne (October 833), presided over by Lothair himself. Louis was deposed; but six months later he was restored to the throne, and Lothair, after brief resistance, had to submit (834) and return to Italy. In the new division (Worms, June 838) Lothair was confirmed in Italy and a strip of territory extending westward as far as the Rhône, the Saône, and the Meuse. Important was the treaty concluded by Lothair with Venice, known as the *Pactum Lotharii* (22 February 840), which regulated mutual relations in the region. Upon the death of his father (20 June 840), Lothair claimed the Empire in the form envisaged by the Constitution of 817, but after the Battle of Fontenoy (25 June 841) he abandoned the struggle and finally reached an agreement with his brothers through the Treaty of Verdun (August 843). His capitulary *De expeditione contra Saracenos facienda* became famous. Broken by remorse and disappointments, he died in the monastery of Prüm wearing the monastic habit, and was succeeded by his son Louis II, to whom he had entrusted the Kingdom of Italy as early as 844.
LOTHAIR I, Emperor, King of Italy — Miniature (9th–10th century) contained in the Martyrology of Wandelbert of Prüm — Vatican Library, cod. Pal. lat. 438, fol. IV. 
LOTHAR III of Supplinburg, Roman Emperor, King of Germany. — Elected at Mainz on 30 August 1125, died in the Tyrol at Breitwang on 4 December 1137. He was of low nobility but had risen to power through the protection of Henry V, whom he had aided in the rebellion against his father. His reward had been the Duchy of Saxony and later the Margraviates of Meissen and Lusatia; however, he later opposed the Emperor. Upon Henry V’s death, the Archbishop of Mainz, Adalbert, turned his sights on Lothair to counter the candidacy of Frederick of Swabia, the nephew of the deceased emperor. At his election some papal legates were present, and Lothair was regarded as the protégé of the Church. His election provoked discontent in various regions of Germany; Frederick of Swabia declared his opposition and proceeded against him harshly, placing him under the imperial ban. Frederick then ceded his rights to his brother Conrad, who had himself elected king by his supporters and then came down to Italy to be recognized as king and crowned in Milan.
The struggle between the two rivals lasted a long time; only in 1135 did Frederick and Conrad of Swabia submit and acknowledge Lothair’s superiority. Lothair had prevailed thanks to the support of Pope Innocent II. Indeed, when in 1130, at the death of Honorius II, the college of cardinals divided and there were the two elections of Innocent II and Anacletus II, Lothair, following the example of France and England, recognized Innocent II as the true pope, who enjoyed the influential favor of St. Bernard. At the Congress of Liège (1131) Lothair and Innocent II reached an agreement: the Pope recognized Lothair as king and promised to crown him emperor once he had been restored to Rome by royal forces and driven out the antipope. Innocent II, however, refused to abandon the Concordat of Worms, as Lothair desired.
Lothair came down to Italy in 1132 and, together with St. Bernard, conducted the Pope into Rome, where he was crowned emperor at St. John Lateran (4 June 1133), since St. Peter’s was occupied by the partisans of Anacletus II. The question of the Concordat of Worms was again discussed, but Innocent II and St. Bernard were firm in its defense. Instead, the matter of the Matilda lands was settled: Lothair was to hold them as a fief, and likewise after him his son-in-law, the Duke of Bavaria; upon their deaths, they were to revert to the Holy See.
Lothair returned to Italy in 1136 at the appeal of Innocent II, who had become isolated in the face of the bloc formed by Anacletus II and his protector Roger II, King of Sicily. This time it was necessary to avoid Rome altogether: at San Severo Lothair and Innocent II jointly invested Rainulf of Alife with the Duchy of Apulia; then they advanced as far as Bari, but Roger II withdrew to Sicily, avoiding battle, and Lothair’s expedition failed. He died on the return journey to Germany.