By the late 19th century, the citadel had become obsolete as a fort, replaced by the twelve forts of the Fortified Position of Liège, though it continued in use as a barracks and as a command post for the Fortified Position, contributing to the country's National Redoubt.

Around the year 1000, during the reign of Notker, Prince-Bishop of Liège, the city built its first walls in sandstone.

The enclosure was shaped like an elongated rectangle of about 25 hectares (62 acres), surrounded with a ditch and lined with towers and gates.

In the early 12th century Holy Roman Emperor Henri IV proposed a larger enclosure, but failed to raise the necessary funds.

In May 1212 the still uncompleted walls were scaled by the troops of Henry I, Duke of Brabant, who sacked the city.

[1] In 1255 Prince-Bishop Henri de Gueldre built the Porte Sainte Walburga, furnished with towers, a well, a drawbridge and a prison, which was in effect the first citadel on the site.

In 1650 the Holy Roman Emperor granted Prince-Bishop Maximilien Henri de Bavière permission to build a fort.

This system employed light troops supported by artillery, reflecting van Coehoorn's lack of interest in fortifications.

[1] With the commencement of the War of Spanish Succession in 1701, the engineer Jacques de la Combe was delegated by Vauban to repair the citadel.

Vauban came to Liège to try to convince Prince-Bishop Joseph Clemens of Bavaria to underwrite the cost of repairs.

A command post for the Fortified Position of Liège was established in the southern portion of the citadel, in a section which survives.

[2] The command post was augmented after World War II with an air intake tower equipped with filters for nuclear, biological and chemical contaminants.

The Enclos des Fusillés ("enclosure of those shot by firing squad") was dedicated in 1947, with 197 crosses commemorating the dead.

Due to the presence of underground excavations, the hospital was placed on driven piles for support.