Barrois, ancient county, then duchy, on the western frontier of Lorraine, a territory of the Holy Roman Empire, of which Barrois was long a fiefdom or holding before being absorbed piecemeal by France. The centre and capital was the town that later came to be known as Bar-le-Duc, in the modern French département of Meuse.
Because of its location between France and Germany, the dukedom was for many years of uncertain loyalty. In 951 the German emperor Otto I gave the countship of Barrois (i.e., the district of Bar), at the time a fief of the duchy of Lorraine, to Frederick of Ardenne. When Frederick’s great-great-grandson Renaud (Reynald) inherited the countship, he founded the House of Bar. The counts of Bar increased their wealth and became the most powerful vassals of the dukes of Lorraine, with whom, however, they carried on endless struggles, usually fighting in the French ranks, while the dukes adhered to the Germans. Count Henry III made an alliance with Edward I of England and the German king Adolf of Nassau against France. Defeated in battle with the French, Henry III was forced in 1301 to do homage to the French king Philip IV for that part of the Barrois west of the Meuse River, which was claimed as being in the mouvance, or feudal dependency, of France and which from then on was called the “Barrois mouvant.”
In 1354 Robert of Bar took the title of duke of Bar. In 1420 René of Anjou, who had inherited the dukedom, married Isabella, heiress of the Duke of Lorraine, so that on the death of the latter (1431) the Barrois and Lorraine were united. From then on the Barrois shared the fate of Lorraine, which was annexed to the French crown in 1766 on the death of Stanisław Leszczyński, the former king of Poland, to whom it had been granted in 1738.