A growing trade center by the 10th cent., Liège became the capital of the extensive prince-bishopric of Liège, which included most of Liège prov. and parts of Limburg and Namur provs. This ecclesiastical state, part of the Holy Roman Empire, lasted until 1792. The strongly fortified city, key to the Meuse valley, suffered numerous sieges in its history. In the Middle Ages, Liège was a leading cultural center with important textile and metal industries.
In the late Middle Ages it was torn by bitter social strife. In the 14th cent. the workers (organized in guilds) won far-reaching concessions from the nobles and the wealthy bourgeoisie and began to take part in the city's government. The episcopal functionaries were placed (1373) under the supervision of a tribunal of 22 persons, 14 of whom were burgesses. This Peace of the Twenty-Two remained, albeit with interruptions, the basic guarantee of the constitutional liberty of the inhabitants of Liège until 1792. In 1465 the city became a protectorate of Burgundy; two years later, Charles the Bold, duke of Burgundy, abolished the citizens' communal liberties. The citizens of Liège, encouraged by Louis XI of France, rose in rebellion, but Charles forced Louis to assist him in suppressing the revolt and then sacked the city (1468).
As an episcopal principality, Liège remained technically a sovereign member of the Holy Roman Empire after the Netherlands passed (1477) under Hapsburg rule (see Netherlands, Austrian and Spanish). In fact, however, the prince-bishops were dependent on the Spanish kings and, after 1714, the emperors. Liège flourished under prince-bishop Erard de la Marck in the 16th cent. and became a center for arms manufacture. In 1792 the French under Dumouriez entered the city. In the 19th cent., Liège was a center of Walloon particularism (see Walloons), rapid industrial growth as one of the earliest modern steelmaking centers, and social unrest.
In World War I its fortifications, reputed to be among the strongest in Europe, fell (1914) to the Germans after a 12-day siege. In World War II, Liège was again taken (May, 1940) by the Germans. It was liberated (May, 1944) by U.S. forces, but during the Battle of the Bulge (Dec., 1944–Jan., 1945) it suffered considerable destruction from German rockets. In the 1950s and 60s, the decline of the steel industry led to massive unemployment, and Liège was again a center of social and political unrest.