Henry III, 1017–56, Holy Roman emperor (1046–56) and German king (1039–56), son and successor of Conrad II. He was crowned joint king with his father in 1028, and acceded on Conrad's death in 1039. Under Henry III the medieval Holy Roman Empire probably attained its greatest power and solidity. In 1041, Henry defeated the Bohemians, who had been overrunning the lands of his vassals, the Poles, and compelled Duke Bratislaus I of Bohemia to renew his vassalage. Although several expeditions to Hungary against the raiding Magyars failed to establish his authority in that country, Henry was able in 1043 to fix the frontier of Austria and Hungary at the Leitha and Morava rivers, where it remained until the end of World War I. In the West, Henry attempted with some initial success to control particularist tendencies among the duchies. The dukes of Saxony and Lorraine (Lotharingia) offered the most resistance. In Saxony, Henry managed to avert rebellion, which, however, erupted after his death. On the death of Duke Gozilo of Lorraine (1044), Henry divided the duchy between the duke's two sons. Duke Godfrey, the elder, who received Upper Lorraine, organized numerous revolts against Henry; in 1047–50 the counts of Holland and Flanders (Lower Lorraine) joined in the revolt. Godfrey was successively defeated, imprisoned, restored, and expelled again. He went to Italy (1051), where he married (1054) Marchioness Beatrice of Tuscany, mother of Matilda; Godfrey used his Tuscan position to bolster his strength in Germany, and Henry was unable to subdue him. Despite his political involvement Henry made religious matters his prime concern and supported monastic reform movements, including the Cluniac order. He branded as simony the customary payments made to the king by new bishops and in 1046 undertook to reform the church. Descending into Italy, he had three rival claimants to the papacy set aside at the synods of Sutri and Rome and was accorded the decisive vote in papal elections. The four German popes named by Henry (including Leo IX) renewed the strength of the papacy, which was to prove the nemesis of his successors. On his death his wife Agnes of Poitou assumed the regency for his infant son, Henry IV.