During Easter of 781, while Charlemagne was in Rome he learned of the rebellion of Tassilo, the duke of Bavaria. Tassilo had once been conquered by the Franks under Pepin the Short. Now he was making a fresh bid for independence with the eager support of his wife, Liutberg, who was the daughter of Charlemagne’s bitter enemy, King Desiderius of the Lombards.
With the backing of the pope, Charlemagne called upon Tassilo, who was also his own cousin, to respect his pact with the Franks. Seeming to acquiesce, Tassilo attended a general assembly at Worms and renewed his fealty to the Carolingian monarch. His submission was a pretense, and, as soon as the Franks appeared to be pressed in Saxony, he rebelled.
This lasted for three years, until 785, when Charlemagne launched a three-sided attack against him. From Trentino he dispatched a column of Lombards commanded by his ten year old son, Pepin; from the Danube he unleashed a combined force of Austrasians, Saxons and Thuringians which advanced on Ratisbon; and from the west the king himself led a Frankish contingent along the Neckar Valley to Lech. Tassilo was trapped, and in a public gathering he yielded his command to Charlemagne.
Charlemagne in exchange for an oath of fealty presented Tassilo a horse with a gold saddlecloth. Evidently, he hoped that his magnanimity would command the permanent allegiance of the difficult duke, but no sooner had Charlemagne begun his return to his own court than Tassilo revolted again. This time, however, his own men refused to follow him, and Tassilo was finished. He was accused of renewed disloyalty and condemned to death. Charlemagne commuted the sentence to life imprisonment, to be served at the monastery at Jumieges.