Fortified position of Liège

The fortified position of Liège was established following World War I by Belgium to block the traditional invasion corridor from Germany through Belgium to France. The Belgian experience of World War I, in which the Belgian Army held up the invading force for a week at Liège, impeding the German timetable for the conquest of France, caused Belgium to consider a refined defence strategy. Belgium upgraded the existing fortifications of Liège and extended them onto the Herve plateau closer to Germany, using the most advanced fortifications available to Belgian military technology. However, in 1936, Belgium's neutrality was proclaimed by King Leopold III of Belgium in a vain attempt to forestall another conflict, preventing France from being able to make active use of the Belgian defences and territory in the forward defence of France. At the outbreak of World War II, Belgium's defences had to resist alone until France could advance into Belgium after neutrality failed. Again the fortifications could not hold the Germans.

The position fortifiée de Liège (PFL) was divided into the modern defensive line, anchored on the Albert Canal by Fort Eben-Emael and extending to the south through a planned five additional forts, designated PFL I, and the ring of forts around Liège itself. Liège commanded crucial road and rail crossings of the Meuse, and remained as strategically important in the 1930s as in 1914. The modernized Liège forts were designated PFL II.

The Liège fortress ring
The first modern forts at Liège were built between 1888 and 1891 at the initiative of Belgian General Henri Alexis Brialmont. The forts made a belt around Liège at a distance of about 7 km from the city centre. Following the Franco-Prussian War, both Germany and France had extensively fortified their new frontiers in Alsace and Lorraine. Belgium's comparatively undefended Meuse valley provided an attractive alternative route for forces seeking to invade either France or Germany. The plains of Flanders could provide transportation, food and fuel for an invading force. Brialmont recognized that France and Germany would once again go to war. Fortifications at Liège and Namur might dissuade France and Germany from fighting their next war in Belgium. The Liège fortifications were intended to deter Germany, while the Namur forts were to dissuade the French.

The forts were built using a small set of basic plans, with standardised details. Forts were typically triangular to minimise the number of defensive batteries in the forts' defensive ditches, presenting their apex to the enemy. Construction began on 28 July 1888. The work was carried out by a French consortium, Hallier, Letellier Frères and Jules Barratoux. All of the new forts were built of concrete, a new material for the time, and were equipped with the most modern arms available in 1888. The concrete was poured, without reinforcement. Lack of sufficient nighttime illumination in the 1880s meant that concrete could only be poured in daylight, causing weak joints between partially cured daily pours. The forts' heavy 12 cm, 15 cm and 21 cm guns were made by the German Krupp firm, and were housed in armoured steel turrets made by various French, Belgian and German firms. The forts of Liège and Namur mounted a total of 171 heavy guns, at an overall cost of 29 million Belgian francs. Lighter 57mm guns provided close defence. The forts were each equipped with a steam-powered electrical generating plant powering lights, pumps and searchlights.

The Brialmont forts were designed to resist shellfire equalling their heaviest guns: 21 cm. The top of the central massif used 4 m of unreinforced concrete, while the caserne walls, judged to be less exposed, used 1.5 m. Under fire, the forts were damaged by 21 cm fire and could not withstand heavier artillery.

Twelve First World War forts
Starting from the north, right bank of the Meuse:
 * Fort de Barchon, large fort modernized for PFL II
 * Fort d'Évegnée, small fort modernised for PFL II
 * Fort de Fléron, large fort modernised for PFL II
 * Fort de Chaudfontaine, small fort modernised for PFL II
 * Fort d'Embourg, small fort modernised for PFL II
 * Fort de Boncelles, large fort modernized for PFL II
 * Fort de Flémalle, large fort modernised for PFL II/IV
 * Fort de Hollogne, small fort used for munitions storage in PFL II
 * Fort de Loncin, large fort, destroyed in World War I
 * Fort de Lantin, small fort, not re-used
 * Fort de Liers, small fort used for munitions storage in PFL II
 * Fort de Pontisse, large fort modernised for PFL II/IV

Two older strongpoints were de-rated in 1891 and played no significant role in either war:
 * The Citadel of Liège
 * The Fort de la Chartreuse

Two additional Brialmont forts were planned, one at Visé, where the Meuse could be forded near Lixhe, on the Dutch frontier. The other fort was planned to go between Namur and Liėge at Huy, to block movement along the Meuse between the cities. Neither was built.

The Liège forts in 1914


War came in 1914, and Liège became the early focus of German attack on the way to France. The forts were known to have shortcomings in their ability to resist heavy artillery, and had never been modernised. During the Battle of Liège the forts were pounded by heavy German artillery of 21 cm, 28 cm and 42 cm. The forts had never been designed to resist such heavy artillery. The bombardment exposed the forts' shortcomings in living arrangements, sanitation, ventilation, construction and protection, culminating with the explosion of the Fort de Loncin under bombardment. Even before this the forts had begun to surrender one by one as they became uninhabitable and unable to respond to attack. German forces defeated the troops assigned to defend the intervals between forts, penetrating to Liège and taking it before the first fort had surrendered.

The forts' mission was to delay the progress of an enemy for the time required for the Belgian Army to mobilise. Left to themselves, the forts were planned to resist a siege for about a month, based on estimates made in 1888. In 1914 the forts were completely outclassed by the much more powerful German artillery, which included the enormous Big Bertha 42 cm howitzer. It was therefore a surprise that the forts resisted as long and as successfully as they did. However, the forts' poor ability to deal with powder gases, pulverized dust and the stench from inadequate sanitary facilities became a determining factor in the endurance of the forts' garrisons. None of the forts, apart from the Fort de Loncin, possessed forced ventilation.

The Belgian forts made little provision for the daily needs of their wartime garrisons, locating latrines, showers, kitchens and the morgue in the fort's counterscarp, a location that would be untenable in combat. This had profound effects on the forts' ability to endure a long assault. These 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. This arrangement was calculated to place a weaker side to the rear to allow for recapture by Belgian forces from the rear, and in an age where mechanical ventilation was in its infancy, allowed natural ventilation of living quarters and support areas. However, the concept proved disastrous in practice. Heavy shellfire made the rear ditch untenable, and German forces were able to get between the forts and attack them from the rear. The massive German bombardments drove men into the central massif, where there were insufficient sanitary facilities for 500 men, rendering the air unbreathable, while the German artillery destroyed the forts from above and from the rear.

Battle of Liège
In the Battle of Liège the Liège fortifications fulfilled their role, stopping the German army long enough to allow the Belgian and French armies to mobilize. The battle revealed shortcomings in the performance of the forts and in the Belgian strategy. The forts themselves suffered from inherent weakness of construction through poor understanding of concrete technology, as well as overall inadequate protection for the garrison and ammunition stores from heavy-caliber artillery bombardment. Unbreathable air from bombardment, the fort's own gun gases and from human waste compelled the surrender of most of the positions. However, the days-long delay caused by the fortress ring allowed the Belgian, and more importantly, the French armies to complete their mobilizations. Had the Germans captured Liège as they had hoped, by a bold stroke, the German army could have been in Paris before France could organize its defence at the First Battle of the Marne.

Position Fortifiée de Liège (PFL)
The Fortified Position of Liège was conceived by a commission charged with recommending options for the rebuilding of Belgium's defences. The 1927 report recommended the construction of a line of new fortifications to the east of the Meuse. Work was seriously delayed by budget crises, forcing work on all fortifications but Eben-Emael to be delayed. Work finally began on the forts at Battice, Aubin-Neufchâteau and Tancrémont in 1933. Two other planned positions were never pursued, with Aubin-Neufchâteau taking over the role of forts planned at Mauhin and Les Waides. There were five layers to the system:
 * Positions avancées: 66 small bunkers positioned close to the border as a delaying position.
 * PFL I: Four modern forts supported by 178 bunkers.
 * PFL II: The southern and eastern portions of the Brialmont fortress ring around Liège, modernized and provided with interval bunkers and anti-tank obstacles. There were 62 infantry shelters and 6 forts in this section.
 * PFL III: Small fortifications defending three crossings of the Meuse, comprising 42 bunkers on the eastern side of the river.
 * PFL IV: Three layers of defences on the west side of the Meuse, comprising a line on the Meuse with 31 bunkers, a line on the Albert Canal with nine bunkers, and ten bunkers with the Forts de Pontisse and Flémalle.

PFL II
The Belgians initially rebuilt eight forts of the ring to the south and east of Liège, with later work on the west side of the fortress ring. It was not possible to repair the Fort de Loncin, which had been completely destroyed by its own magazines in 1914. The improvements addressed the shortcomings revealed by the Battle of Liège, allowing the fortress ring to be a backstop to the primary line of fortifications farther east. The Liège ring was designated PFL II, although the forts on the west side of the river were part of PFL IV.

Improvements included replacing 21 cm howitzers with longer-range 15 cm guns, 150mm howitzers with 120mm guns, and adding machine guns. Generating plants, ventilation, sanitation and troop accommodations were improved, as well as communications. The work incorporated alterations that had already been made by the Germans during their occupation of the forts in World War I. Most notably, the upgraded forts received defended air intake towers, intended to look like water towers, that could function as observation posts and emergency exits.

PFL I
Four new forts were built about 20 km to the east of Liège, of a planned six. In contrast to the ring of forts protecting Liège, the new fortification line was similar in concept to the French Maginot Line: a series of positions in a line along the frontier, intended to prevent an enemy advance into Belgian territory, rather than to defend a specific strong point. This new line was designated PFL I, the primary defence line against an advance from Germany, as well as a German advance through Dutch territory at Maastricht. Fort Eben-Emael was positioned to defend the water obstacle of the Albert Canal and to anchor the northern end of the line, with a field of fire all the way north to Maastricht. The Fort de Battice occupied the second strategic point on the main road and rail lines from Aachen. The forts de Tancrémont and Aubin-Neufchâteau filled in the intervals. The cancelled Fort de Sougné-Remouchamps was to be similar to the smaller forts, while plans for two small forts at Comblain-du-Pont and Les Waides were abandoned early in the planning process. The big forts had as many as 2000 men, the smaller 600.

While the organization of the overall defensive line mimicked the Maginot Line, the design of the individual forts was conservative. In contrast to the French fortifications, distributed along a single main gallery in the fort palmé concept, the Belgian forts remained a set of powerfully-armed, tightly grouped combat blocks surrounded by a defended ditch. Eben-Emael and Battice featured 120mm gun turrets with a range of 18 km, and all four forts were equipped with 75mm gun turrets (10 km) and French 81mm mortars in pit emplacements. Eben-Emael, with its site along the artificial cliff of the Albert Canal cutting, was the only fort to be equipped with artillery casemates. The sheer face also provided a naturally-defended location for the fort's air intakes. The new forts featured extreme levels of concrete and armour protection, with between 3.5 m and 4.5 m of concrete cover and up to 450 mm of armour on turrets. Learning from World War I, the intervals between forts were liberally supplied with observation positions and infantry shelters.

Forts built before the Second World War
Starting from the north
 * Fort Eben-Emael
 * Fort d'Aubin-Neufchâteau
 * Fort de Battice
 * Fort des Waides near Manaihant, Herve commune (planned, not built)
 * Fort de Tancrémont or Pepinster
 * Sougné-Remouchamps (planned)

Personnel
In 1940 the Fortified Position of Liège was commanded by Colonel Modart, assisted by Colonel Rosa. They commanded five regiments:
 * 1st Liègeois Fortress Regiment: Eben-Emael
 * 2nd Liègeois Fortress Regiment: Pontisse, Barchon and Aubin-Neufchâteau
 * 3rd Liègeois Fortress Regiment: Evegnée and Fléron
 * 4th Liègeois Fortress Regiment: Chaudfontaine, Embourg, Boncelles, Flémalle and Tancrémont
 * 5th Liègeois Fortress Regiment: Battice

Second World War battles
The Belgian command was counting on Eben-Emael to be the key defense of the northern frontier at Liège. It naturally attracted the first German attacks. Its enormous dimensions dictated an unconventional attack strategy, using airborne troops. The fort was attacked on 10 May 1940 and rendered ineffective in a few hours by a team of 75 men armed with new shaped-charge explosives. Ineffective Belgian defense of the fort's surface allowed the German assault team to use their explosive charges to destroy or render the fort's gun turrets and machine gun cloches uninhabitable.

With Eben-Emael out of action, the Germans could attack the other new forts with more conventional means, continuing attacks from 10 May. The forts of both PFL I and II attempted to support each other with covering fire, but to little effect. The PFL I forts quickly fell, with Battice and Aubin-Neufchâteau surrendering on 22 May. Tancrémont was bypassed.

The PFL II forts were assaulted starting 12 May after Belgian field forces retreated from Liège. Isolated, the forts fought on. Fort de Flémalle came under air attack on 15 May, surrendering the next day. On 18 May Fort de Barchon was assaulted by the same infantry battalion that had attacked Eben-Emael, supported by a 420mm howitzer. The fort surrendered the same day, as did Fléron and Pontisse. Evengnée surrendered on 20 May. The other forts to the south were bypassed and surrendered on 28 May, part of the general Belgian surrender. Tancrémont held out until the next day, the last fort to surrender.

During the Second World War Eben-Emael was abandoned, apart from use for propaganda films and weapons effects experiments, including armor-piercing shells. Battice and Aubin-Neufchâteau were also used for these experiments.

Present day
Of the dozen Brialmont forts, seven are open to the public and may be visited – Loncin, Lantin, Flémalle, Hollogne, Pontisse, Barchon and Embourg. Chaudfontaine may also be visited under certain circumstances, but has not been rehabilitated. The Fort de Loncin has since the explosion of 15 August 1914, been a military cemetery and memorial. The Fort de Lantin has been extensively restored, and since it was not re-armed between the wars, it presents the appearance of an 1888 fort.

Other forts have been partially buried (Fléron, Boncelles) and are not visitable, apart from the air intake tower of Boncelles. Others are supply depots for the Belgian Army.

The four inter-war forts are in varying states of preservation, though all may be visited. Tancrémont is notably intact, with all equipment present. Eben-Emael and the others remain military property, but Eben-Emael is administered by the Association Fort Eben-Emael as a museum.