BOUILLON, formerly the seat of a dukedom in the Ar dennes, now a small town in the Belgian province of Luxembourg. Pop. (193o) 2,869. It is picturesquely situated in the valley of the Semois, under the rocky ridge which preserves remains of the castle of Godfrey of Bouillon (q.v.), the leader of the first crusade. The stream almost encircles the castle, which provides beautiful views of the sinuous valley. In the 8th and 9th centuries Bouillon was one of the castles of the counts of Ardennes and Bouillon. Later, the family took the higher titles of dukes of Lower Lorraine and Bouillon, who all bore the name of Godfrey (Godefroy), and the fifth of them was the great crusader. In order to undertake the crusade, Godfrey sold the castle of Bouillon to the prince bishop of Liege, and the title of duke of Bouillon belonged to the bishopric till 1678. The bishops appointed "chatelains," one of whom was the celebrated "Wild Boar of the Ardennes," William de la Marck, and his descendants, "princes of Sedan and dukes of Bouillon," became semi-independent. The possession of Bouillon thenceforward became a constant cause of strife until in 1678 Louis XIV. garrisoned it under the treaty of Nijmwegen. Bouillon remained French till 1814, and Vauban called it "the key of the Ardennes." In 1760 the elder Rousseau established here the famous press of the Encyclopaedists. By the Vienna Congress (1815) Bouillon went to the Netherlands.