The ruins of the medieval fortress in Bouillon, dated from the 8 - 10th century.  Godefroy from Bouillon sold the castle in 1096, to finance his participation in the first crusade.  He had the option however to buy it again within three years from the prince-bishop of Liège - the latter had robbed his own churches to be able to pay Godefroy.  Godefroy made it to Jerusalem and died there in 1100.