Charlemagne now realized that the time had come for him to deal with Thassilo, Duke of Bavaria, a somewhat difficult matter because of their near relationship, Thassilo being, as already stated, Pepin’s nephew. The Duke was not only secretly conspiring against Charlemagne in Italy, but he was also in communication with the leaders of the Slavs and Thuringians, urging them to resist Charlemagne’s authority. His most serious offence, however, was his effort to induce the Avars[37] to assist in the war against the King.  
59
Charlemagne, learning of the intrigues in Italy, appeared there much sooner than his enemies had anticipated, and easily thwarted their designs; after which he went to Rome and attended the Easter festival (787). Fearing that Charlemagne might discover all his secret plottings, Thassilo sent messengers to the Pope asking him to take steps to bring about a reconciliation between himself and the King. The Pope, however, uncertain whether he was in earnest or simply wished to gain time, not only refused to comply with his request, but sent word to him that if he violated his solemn promises or evaded them in any way the ban would be pronounced against him.
 
After his return Charlemagne summoned a parliament at Worms and laid Thassilo’s case before it. His refusal to appear only aggravated his guilt. War was declared against him. Three Frankish armies invaded Bavaria, two of them led by the King’s sons, Carl and Pepin, the third by Charlemagne in person. Thassilo was taken by surprise, for he had intended to begin his operations later. Neither the discontented Thuringians, who were in league with him, nor the Slavs and Avars, came to his help. Thassilo’s wife, Luitberger, daughter of Desiderius, had persistently urged her husband to make war against Charlemagne, and when too late she realized the folly of her advice and the danger which threatened Thassilo. The Bavarians themselves were not eager to fight, and indeed expressed more confidence in Charlemagne than in their Duke. Under these discouraging circumstances Thassilo deemed it wisest to betake himself to Charlemagne’s camp and implore his pardon. He was exceedingly penitent and tendered his sceptre to the King, saying that he had forfeited any right to hold it longer. Charlemagne invested Thassilo with the dukedom in fee and took hostages from him, among them his son, Theudo.
 
60
Delighted that he had escaped this danger, Thassilo went to Regensburg and Charlemagne returned home. But Thassilo had hardly come under his wife’s influence again when he violated his promise and resumed his hostile machinations. He summoned the leaders of his people to Regensburg, denounced his royal cousin, reviled him, and openly declared he would not respect a compulsory promise even if it cost him ten sons. The foolish Duke did not realize how contemptible he made himself by his conduct in the eyes of all honest men. He renewed negotiations with the Avars and induced them to join him. One division of the barbarians was led by Thassilo through Bavarian territory into the Frankish kingdom, and a second into Italy; but both armies were defeated by Carl, who was sent against them by the King.
 
61
Justice at last overtook Thassilo. He was summoned to appear before the Parliament at Ingelheim. The defeat of the Avars had so completely demoralized him that he did not dare to disobey the summons. He failed to clear himself from the charge of treason. His own followers testified against him. The indictment against him which called for the severest penalty was based upon this article in the Frankish statutes: “Whoever shall fail to keep faith with the kingdom, whoever shall break his vows to the King, whoever shall ally himself with the enemies of the kingdom, shall forfeit his life.” The death penalty was unanimously pronounced. Charlemagne asked him what he would do if his life were spared; whereupon Thassilo, as a proof of his repentance, agreed to spend the rest of his days in a monastery, received the tonsure at St. Goar, and was sent from there to Fulda.[38] Charlemagne declared his ducal title extinguished, assigned Frankish counts to the districts of Bavaria, and incorporated it in the Frankish kingdom.
 
The year 790 was one long remembered by the Franks, for it was the only peaceable year in Charlemagne’s long reign. Preparations, however, had to be made to punish the Avars and prevent raids in future.
 
62
The Avars, living between the Enns[39] and the Sau,[40] were of Hunnish stock, for which reason they are sometimes called Huns in the old chronicle. They inherited not only the pillaging habits of their ancestors, who swept over Germany like a deluge in the fifth century, but the almost countless treasures, or a considerable part of the treasure, which their fathers had stolen. The defences which they built on their frontiers were of a peculiar kind. They were called “rings”; each one of them was sufficiently large to enclose a number of villages, and consisted of strong walls, ten feet high and as many wide, constructed of tree-trunks and rocks cemented together and surmounted by densely planted thorn bushes. Behind such walls, the Avars thought they were secure against any enemy; but they were soon to learn their mistake.
 
63
Charlemagne reviewed his forces at Regensburg before entering upon his campaign. Upon this occasion he buckled a sword around his third son Ludwig, then thirteen years of age, who was to take part in the expedition. He moved along both banks of the Danube in an easterly direction, while Pepin made his advance from Italy. The Khan of the Avars attacked the latter and was defeated in a bloody battle. When Charlemagne reached the Enns he heard the news and invaded the enemy’s country at once. Several rings were carried by storm, the contents of the treasure vaults removed, the villages devastated, and large numbers of prisoners were taken. A sickness which broke out among the army horses forced the King to retire sooner then he had intended. The war, however, lasted some years longer before the enemy was entirely subjugated. The decisive battle occurred in the year 796. The rings which Pepin had reconstructed, as well as those which remained in possession of the enemy after the first expedition, were taken by assault. Wien[41] was one of the principal localities occupied by the Avars. Charlemagne made the Avar country the Oestmark of the kingdom, subsequently called Oesterrichi and at a later period Oesterreich.