Fort d ' Illange The Fort d ' Illange is a fortification located to the south of Thionville in the Moselle department of France . It was built by Germany next to the town of Illange in the early 20th century after the annexation of the Moselle following the Franco - Prussian War . The Fort d ' Illange was part of the " Moselstellung " , a group of eleven fortresses surrounding Thionville and Metz to guard against the possibility of a French attack aimed at regaining Alsace and Lorraine , with construction taking place between 1905 and 1911 . The fortification system incorporated new principals of defensive construction to deal with advances in artillery . Later forts , such as Illange , embodied innovative design concepts such as dispersal and concealment . These later forts were designed to support offensive operations , as an anchor for a pivoting move by German forces into France . The Feste Illangen , as Fort d ' Illange was called by the Germans , with Fort de Guentrange and Fort de Koenigsmacker , assured the protection of Thionville against French attack . Positioned to the rear of the principal lines of combat in the First World War , the fort never saw combat in that war , but was captured by advancing American forces in the Lorraine Campaign of World War II . Description . The Fort d ' Illange is located about to the south of Thionville on a hilltop overlooking the Moselle . It was defended by a garrison of 1200 men . Like the Fort de Koenigsmacker , Illange features an armoured battery , originally armed with four short 100mm guns in single turrets . Four separate fortified barracks housed troop , with underground galleries connected the battery , barracks , and infantry positions . The dispersed , un - walled nature of the later " Moselstellung " was a significant innovation . Compared to the French Séré de Rivières system forts of the same era , later German fortifications such as Illange were scattered over a large area and enclosed chiefly by barbed wire . While certain individual elements presented imposing walls to an attacker , these walls were not continuous . The dispersed nature is evidenced by the official French name : the " Groupe Fortifié d ' Illange " ( Fortified Group of Illange ) . These arrangements were studied and improved upon by the French in the construction of the Maginot Line . Illange ' s fairly compact arrangement includes four dispersed fortified barracks built into a hillside so that their rears are shielded by earth , while the tops and fronts are protected by three of four metres of concrete , and are surmounted by parapets . The single battery is similarly constructed and linked to the barracks by underground tunnels at an average depth of 8 to 11 metres , about in length . The four 100mm guns in the battery were protected by Schumann turrets and controlled by two armored observation cupolas on top of the north and south barracks . The east and west barracks are also equipped with cupolas . The whole was surrounded by deep networks of barbed wire , which were swept by fire from small perimeter blockhouses , also linked via the tunnel system . The interior of the position was equipped with trenches for infantry . The barracks and batteries were further armoured with reinforced concrete and armored windows . A variety of blockhouses and infantry shelters were also built in the intervals between forts . The barracks and armored batteries featured central heating , while electricity was provided from a central utility plant equipped with five 45 hp diesel engines . Operational concept . From 1899 , the Germans viewed Metz as a secure position that could provide an anchor for a pivoting movement into France from the Low Countries . This strategy , which would become known as the Schlieffen Plan , required that the " Moselstellung " deter an advance by French forces into Lorraine while the German forces mobilized . History . Begun in 1905 , Illange was completed in 1911 and saw no action during World War I , as Thionville remained well within German lines for the duration of the war . Feste Illangen was the headquarters for the Thionville group of fortifications , under Generallieutnant von Lochow . With the Compiègne armistice of 1918 , Lorraine was returned to France and the fort became French property . The three Thionville forts became known as the Fortified Group of Thionville . The Fort d ' Illange was integrated into the Fortified Sector of Thionville of the Maginot Line in the 1930s , serving as the sector ' s command post and backing up the newer Maginot " ouvrages " that were built about halfway between Thionville and the border with Luxembourg . The short 105mm guns were replaced by 105mm long guns removed from the German fortifications of Metz . The artillery range was thus increased from to . During the Battle of France the Thionville area was bypassed and encircled by German forces , with the Maginot and earlier fortifications seeing little action . In 1944 , as the Fort de Koenigsmacker was being subdued to the north , the U . S . 90th Infantry Division approached Illange on 11 November 1944 . A German soldier appeared under a white flag to request terms for evacuating the fort , but was told that the Germans would be required to surrender immediately . The Germans resisted and were kept under bombardment by heavy artillery through the night while combat engineers attacked the fort ' s openings with explosives . The fort surrendered the next morning . Present status . The fort is abandoned and stripped , but the grounds are accessible and have been administered as an open - air museum since 2003 . The buildings and sub - surface works are sealed .