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First Italian Military Expedition

In the early summer of 951, before his father marched across the Alps, Otto's son Liudolf, Duke of Swabia, invaded Lombardy in Northern Italy. The exact reasons for Liudolf's action are unclear, and historians have proposed several possible motives. Liudolf may have tried to help Adelaide, a distant relative of Liudolf's wife Ida, or he intended to strengthen his position within the royal family. The young heir was also competing with his uncle, Duke Henry I of Bavaria, both in German affairs and Northern Italy. While Liudolf was preparing his expedition, Henry influenced the Italian aristocrats not to join Liudolf's campaign. When Liudolf arrived in Lombardy, he found no support and was unable to sustain his troops. His army was near destruction until Otto's troops crossed the Alps. The king reluctantly received Liudolf's forces into his command, angry at his son for his independent actions.

Otto and Liudolf's troops arrived in northern Italy in September 951 without opposition from Berengar II. As they descended into the Po River valley, the Italian nobles and clergy withdrew their support for Berengar and provided aid to Otto and his advancing army. Recognizing his weakened position, Berengar II fled from his capital in Pavia. When Otto arrived at Pavia on 23 September 951, the city willingly opened its gate to the German king, who was crowned king of the Lombards. Otto assumed the titles of Rex Italicorum and Rex Langobardorum in his acts from the 10 October onwards. Like Charlemagne before him, Otto was now concurrent King of Germany and King of Italy. Otto sent a message to his brother Henry in Bavaria to escort his bride from Canossa to Pavia, where the two married.

Soon after his father's marriage in Pavia, Liudolf left Italy and returned to Swabia. Archbishop Frederick of Mainz, the Primate of Germany and Otto's long-time domestic rival, also returned to Germany alongside Liudolf. Disturbances in northern Germany forced Otto to return with the majority of his army back across the Alps in 952. Otto did leave a small portion of his army behind in Italy and appointed his son-in-law Conrad, Duke of Lorraine, as his regent and tasked him with subduing Berengar II.