Otto I The Great King Of Germany was the first king to become Holy Roman Emperor. He became King of Germany in 936 and ruled all of Germany. In 951, he crossed the Alps and declared himself the king of Italy. He was forced to return to Germany when the other German princes began a series of revolts. At the same time the Slavs in Poland and Bohemia revolted, and the Magyars, or Hungarians, invaded Germany. Otto crushed the Magyars in the battle of the Lech River in 955. The Poles and Bohemians were forced to accept his rule. Otto was able to replace most of the rebellious German princes with members of his own family. The young king of Arles, or Burgundy, also had to accept his rule. Otto then turned his attention toward Italy. He married the widow of an earlier Italian king, and defeated a rival for the throne. In 961, Otto crossed the Alps in answer to an appeal from Pope John XII to put down an uprising in Rome. For this service, Otto was crowned in 962 emperor of what was later known as the Holy Roman Empire.