king reasserted his desires for dominion over Italy and to claim the imperial title. He sent emissaries to the Duchy of Lorraine and stirred the local nobles against Conrad's rule. The duke was a Salian Frank by birth and unpopular with the people of Lorraine, so they pledged their support to Otto. Otto's actions at the Diet provoked the people of Swabia and Franconia into rebellion. After initial defeats by Otto, Liudolf and Conrad fell back to their headquarters in Mainz. In July 953, Otto and his army laid siege to the city, supported by Henry's army from Bavaria. After two months of siege, the city had not fallen and rebellions against Otto's rule grew stronger in southern Germany. Faced with these challenges, Otto opened peace negotiations with Liudolf and Conrad. Bruno the Great, Otto's youngest brother and royal chancellor since 940, accompanied his older brothers and oversaw the arrangements for the negotiations. As the newly appointed Archbishop of Cologne, Bruno was eager to end the civil war in Lorraine, which was in his ecclesiastical territory. The rebels demanded ratification of the treaty they had previously agreed to with Otto, but Henry's provocation during the meeting caused the negotiations to break down. Conrad and Liudolf left the meeting to continue the civil war. Angered by their actions, Otto stripped both men of their duchies of Swabia and Lorraine, and appointed his brother Bruno as the new Duke of Lorraine. While on military campaign with Otto, Henry appointed the Bavarian Count Palatine, Arnulf II, to govern his duchy in his absence. Arnulf II was a son of Arnulf the Bad, whom Henry had previously displaced as duke, and he sought revenge: he deserted Henry and joined the rebellion against Otto. Lifting the siege of Mainz, Otto and Henry marched south to regain control over Bavaria. Without the support of the local nobles, their plan failed and they were forced to retreat to Saxony. The duchies of Bavaria, Swabia, and Franconia were in open civil war against the King, and even in his native Duchy of Saxony revolts began to spread. By the end of 953, the civil war was threatening to depose Otto and permanently end his claims to be Charlemagne's successor. Forcing an end to the rebellion In early 954, Margrave Hermann Billung, Otto's long-time loyal vassal in Saxony, was facing increased Slavic movements in the east. Taking advantage of