Giselbert and Fredelon terrorized the region so that the inhabitants could not do basic tasks for survival, such as gathering wood or tilling the soil.
Henri de Verdun, Bishop of Liège, gave the advocacy of this land to the adjacent landowner, Conon, Count of Montaigu, and forced Giselbert and Fredelon to restore the damage they had wrought.
The siege lasted from 29 June to 9 August 1095 and ended unsuccessfully, partly because Godfrey of Bouillon and other nobles in the army refused to attack the castle owing to an unresolved dispute concerning the deposed abbot of Saint-Hubert.
The second is that the activities of the occupants of Clermont in 1095, Giselbert and Fredelon, who some regarded as brigandage, were perceived by these two as the legitimate levying of tolls on river traffic.
The acquisition of Clermont and its subsequent enfeoffment to his vassal Lambert was part of a consistent policy of purchase which also brought to the prince-bishop the important fortresses of Mirwart, Couvin and, Bouillon.