The incorporation of Bavaria with the Frank empire brought a new task to Charlemagne. The Avars, who had gradually extended their rule across the Alps, nearly to the Adriatic, were strong and dangerous neighbors. In 791 he entered their territory and laid it waste, as far as the river Raab; then, having lost all his horses on the march, he was obliged to return. At home, a new trouble awaited him. His son, Pippin, whom he had installed as king of Lombardy, was discovered to be at the head of a conspiracy to usurp his own throne. Pippin was terribly flogged, and then sent into a monastery for the rest of his days; his fellow-conspirators were executed. When Charlemagne applied his system of military conscription to the Saxons, to recruit his army before renewing the war with the Avars, they rose once more in rebellion, slew his agents, burned the churches, and drove out the priests, who had made themselves hated by their despotism and by claiming a tenth part of the produce of the land. Charlemagne was thus obliged to subdue them and to fight the Avars, at the same time. The double war lasted until 796, when the residence of the Avar Khan, with the intrenched "ring" or fort, containing all the treasures amassed by the tribe during the raids of two hundred years, was captured. All the country, as far eastward as the rivers Theiss and Raab, was wasted and almost depopulated. The remnant of the Avars acknowledged themselves Frank subjects, but for greater security, Charlemagne established Bavarian colonies in the fertile land along the Danube. The latter formed a province, called the East-Mark, which became the foundation upon which Austria (the East-kingdom) afterwards rose. [Sidenote: 799.] The Saxons were subjected--or seemed to be--about the same time. Many of the people retreated into Holstein, which was then called North-Albingia; but Charlemagne allied himself with a branch of the Slavonic Wends, defeated them there, and took possession of their territory. He built fortresses at Halle, Magdeburg, and Büchen, near Hamburg, colonized 10,000 Saxons among the Franks, and replaced them by an equal number of the latter. Then he established Christianity for the fifth time, by ordering that all who failed to present themselves for baptism should be put to death. The indomitable spirit of the people still led to occasional outbreaks, but these became weaker and weaker, and finally ceased as the new faith struck deeper root.