Fort de Flémalle was built between 1881 and 1884 according to the plans of General Henri Alexis Brialmont.

The Fort de Flémalle is located about 7 kilometres (4.3 mi) southwest of the center of Liège.

The service areas were placed directly opposite the barracks, which opened into the ditch in the rear of the fort (i.e., in the face towards Liège), with lesser protection than the two "salient" sides.

[3] The Brialmont forts were designed to be protected from shellfire equaling their heaviest guns: 21 cm.

[2] The fort's heavy guns were German, typically Krupp, while the turret mechanisms were from a variety of sources.

When the Liège's fortifications proved unexpectedly stubborn, the Germans brought heavy siege artillery to bombard the forts with shells far larger than they were designed to resist.

[8] Flémalles armament was upgraded in the 1930s to become part of the Fortified Position of Liège II, which was planned to deter a German incursion over the nearby border.

This was accompanied by improvements to ventilation, protection, sanitary facilities, communications and electrical power.

Following the successful German assault on Fort Eben-Emael to the east, Flémalle provided fire support for Belgian field units for the next few days.