soon swore fealty to the new king, but Arnulf of Bavaria did not recognize Henry's position. According to the Annales iuvavenses, Arnulf was elected king by the Bavarians in opposition to Henry, but his "reign" was short-lived; Henry defeated him in two campaigns. In 921, Henry besieged Arnulf's residence at Ratisbon (Regensburg) and forced him into submission. Arnulf had to accept Henry's sovereignty; Bavaria retained some autonomy and the right to invest bishops in the Bavarian church. Heir apparent Otto first gained experience as a military commander when the German kingdom fought against Wendish tribes on its eastern border. While campaigning against the Wends/West Slavs in 929, Otto's illegitimate son William, the future Archbishop of Mainz, was born to a captive Wendish noblewoman. With Henry's dominion over the entire kingdom secured by 929, the king probably began to prepare his succession over the kingdom. No written evidence for his arrangements is extant, but during this time Otto is first called king (Latin: rex) in a document of the Abbey of Reichenau. While Henry consolidated power within Germany, he also prepared for an alliance with Anglo-Saxon England by finding a bride for Otto. Association with another royal house would give Henry additional legitimacy and strengthen the bonds between the two Saxon kingdoms. To seal the alliance, King Æthelstan of England sent Henry two of his half-sisters, so he could choose the one which best pleased him. Henry selected Eadgyth as Otto's bride and the two were married in 930. Several years later, shortly before Henry's death, an Imperial Diet at Erfurt formally ratified the king's succession arrangements. Some of his estates and treasures were to be distributed among Thankmar, Henry, and Bruno. But departing from customary Carolingian inheritance, the king designated Otto as the sole heir apparent without a prior formal election by the various dukes. Reign as king Coronation Henry died from the effects of a cerebral stroke on 2 July 936 at his palace, the Kaiserpfalz in Memleben, and was buried at Quedlinburg Abbey. At the time of his death, all of the various German tribes were united in a single realm. At the age of almost 24, Otto assumed his father's position as Duke of Saxony and King of Germany. His coronation was held on 7 August 936 in Charlemagne's former capital of Aachen, where Otto was anointed and crowned by Hildebert, the Archbishop of Mainz. Though he