Louis the Pious drew up an Ordinatio Imperii, detailing the future of the Frankish Empire. Under this, the bulk of the Frankish territory went to Louis' eldest son, Lothair; Bernard received no further territory, and although his Kingship of Italy was confirmed, he would be a vassal of Lothair. This was, it was later alleged, the work of the Empress, Ermengarde, who wished Bernard to be displaced in favour of her own sons. Resenting Louis' actions, Bernard began plotting with a group of magnates: Eggideo, Reginhard, and Reginhar, the last being the grandson of a Thuringian rebel against Charlemagne, Hardrad. Anshelm, Bishop of Milan and Theodulf, Bishop of Orléans, were also accused of being involved.

Louis the Pious reacted swiftly to the plot, marching south to Chalon. Bernard and his associates were taken by surprise; Bernard travelled to Chalon in an attempt to negotiate terms, but he and the ringleaders were forced to surrender to him. Louis had them taken to Aix-la-Chapelle, where they were tried and condemned to death. Louis 'mercifully' commuted their sentences to blinding, which would neutralize Bernard as a threat without actually killing him; however, the process of blinding (carried out by means of pressing a red-hot stiletto to the eyeballs) proved so traumatic that Bernard died in agony two days after the procedure was carried out.

http://en.wikipedia.org/wiki/Bernard_of_Italy