Otto the Great
Hungarian military invasions

The Hungarians (Magyars) invaded Otto's domain as part of the larger Hungarian invasions of Europe and ravaged much of Southern Germany during Liudolf's civil war. Though Otto had installed the Margraves Hermann Billung and Gero on his kingdom's northern and northeastern borders, the Principality of Hungary to the southeast was a permanent threat to German security. The Hungarians took advantage of the kingdom's civil war and invaded the Duchy of Bavaria in spring 954. Though Liudolf, Duke of Swabia, and Conrad, Duke of Lorraine, had successfully prevented the Hungarians from invading their own territories in the west, the invaders managed to reach the Rhine River, sacking much of Bavaria and Franconia in the process.

The Hungarians, encouraged by their successful raids, began another invasion into Germany in the spring of 955. Otto's army, now unhindered by civil war, was able to defeat the invasion, and soon the Hungarians sent an ambassador to seek peace with Otto. The ambassador proved to be a decoy: Otto's brother Henry I, Duke of Bavaria, sent word to Otto that the Hungarians had crossed into his territory from the southeast. The main Hungarian army had camped along the Lech River and besieged Augsburg. While the city was defended by Bishop Ulrich of Augsburg, Otto assembled his army and marched south to face the Hungarians.

Otto and his army fought the Hungarian force on 10 August 955 at the Battle of Lechfeld. Under Otto's command were Burchard III, Duke of Swabia and Bohemian troops of Duke Boleslaus I. Though outnumbered nearly two to one, Otto was determined to push the Hungarian forces out of his territory. According to Widukind of Corvey, Otto "pitched his camp in the territory of the city of Augsburg and joined there the forces of Henry I, Duke of Bavaria, who was himself lying mortally ill nearby, and by Duke Conrad with a large following of Franconian knights. Conrad's unexpected arrival encouraged the warriors so much that they wished to attack the enemy immediately."

The Hungarians crossed the river and immediately attacked the Bohemians, followed by the Swabians under Burchard. Confusing the defenders with a rain of arrows, they plundered the baggage train and made many captives. As Otto received word of the attack, he ordered Conrad to relieve his rear units with a counter-attack. Upon the successful completion of his mission, Conrad returned to the main forces and the King launched an immediate assault. Despite a volley of arrows, Otto's army smashed into the Hungarian lines and was able to fight them in hand-to-hand combat, giving the traditionally nomadic warriors no room to use their preferred shoot-and-run tactics; the Hungarians suffered heavy losses and were forced to retreat in disorder.

According to Widukind of Corvey, Otto was proclaimed Father of the Fatherland and Emperor at the following victory celebration. While the battle was not a crushing defeat for the Hungarians, as Otto was not able to chase the fleeing army into Hungarian lands, the battle ended nearly 100 years of Hungarian invasions into Western Europe.

While Otto was fighting the Hungarians with his main army deployed in Southern Germany, the Obotrite Slavs in the north were in a state of insurrection. Count Wichmann the Younger, still Otto's opponent over the King's refusal to grant Wichmann the title of Margrave in 936, marauded through the lands of the Obotrites in the Billung March, causing the followers of Slavic Prince Nako to revolt. The Obotrites invaded Saxony in the fall of 955, killing the men of arms-bearing age and carrying off the women and children into slavery. In the aftermath of the Battle of Lechfeld, Otto rushed to the north and pressed far into their territory. A Slav embassy offered to pay annual tribute in return for being allowed self-government under German overlordship instead of direct German rule. Otto refused, and the two sides met on 16 October at the Battle of Recknitz. Otto's forces gained a decisive victory; after the battle, hundreds of captured Slavs were executed.

Celebrations for Otto's victory over the pagan Hungarians and Slavs were held in churches across the kingdom, with bishops attributing the victory to divine intervention and as proof of Otto's "divine right" to rule. The battles of Lechfeld and Recknitz mark a turning point in Otto's reign. The victories over Hungarians and Slavs sealed his hold on power over Germany, with the duchies firmly under royal authority. From 955 on, Otto would not experience another rebellion against his rule and as a result was able to further consolidate his position throughout Central Europe.

Otto's son-in-law, Conrad, the former Duke of Lorraine, was killed in the Battle of Lechfeld and the king's brother Henry I, Duke of Bavaria, was mortally wounded, dying a few months later on 1 November of that year. With Henry's death, Otto appointed his four-year-old nephew Henry II, to succeed his father as duke, with his mother Judith of Bavaria as his regent. Otto appointed Liudolf in 956 as the commander of an expedition against King Berengar II of Italy, but he soon died of fever on 6 September 957. Archbishop William buried his half-brother at St. Alban's Abbey near Mainz. The deaths of Henry, Liudolf, and Conrad took from Otto the three most prominent members of his royal family, including his heir apparent. Additionally, his first two sons from his marriage to Adelaide of Italy, Henry and Bruno, had both died in early childhood by 957. Otto's third son by Adelaide, the two-year-old Otto, became the kingdom's new heir apparent.
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