return from Bohemia. The Emperor, aided by the Duke of Swabia and Bavaria, met the rebels at Passau and, after a long siege, forced them into submission. Otto II then brought the rebels before the Imperial Diet in Quedlinburg on March 31, 978. Boleslaus II was treated with honors and swore loyalty to Otto II. Mieszko I of Poland recognized Otto's royal authority to the throne. Otto II imprisoned Henry II under the custody of the Bishop of Utrecht where he would remain until Otto II's death in 983. While Otto the Great had pardoned rebellious family members for their crimes, Otto II followed a different policy. Instead, Otto II hoped to subordinate the Bavarian line of Ottonians to his Imperial authority. Henry II's four-year-old son, also named Henry, was sent to Hildesheim to study for an ecclesiastical career. It appears Otto II intended to end the Bavarian Ottonians' secular control of Bavaria. Under a new Duke, Bavaria would remain a remote area of the Empire. Otto II would only visit the Duchy three times during his reign, in all cases accompanied by the military. War with Denmark In 950, Otto the Great had subdued the Kingdom of Denmark and forced the Danish King Gorm the Old to accept him as his overlord. Otto the Great also forced the king and his heir apparent Harald Bluetooth to convert to Christianity. Under the reign of Otto the Great, Denmark fulfilled all its obligations and regularly paid tribute to the Germans. When Harald became king in 958, he expanded the control of his kingdom into Norway, becoming king there in 970. With his newly obtained power, the young ruler was no longer willing to accept German supremacy over his kingdom. In summer 974, Harald rebelled against Otto II. With the support of Norwegian troops, Harald was able to cross the Danish border into Germany, defeating the German forces stationed in the north. Otto II attacked Harald's forces, but the joint Danish-Norwegian army repelled the German army. In autumn, however, when the Norwegian allies sailed north to return to Norway, Otto II was able to counter Harald's advances at the Danevirke. War against France Before Henry II's civil war in southern Germany erupted, Otto II was faced with disputes in western Germany. The brothers Reginar IV, Count of Mons, and Lambert I, Count of Louvain, demanded that the Emperor restore their confiscated inheritance