Fort de Charenton Fort de Charenton is a fortification built in 1842 in the community of Maisons - Alfort , and part of the Paris defences planned by Adolphe Thiers . After the fall of Napoleon I in 1814 , and again after Napoleon ' s defeat at Waterloo in 1815 , Paris was occupied by foreign forces . To counter new invasion and occupation , defensive works were planned . In 1841 a new fortified enclosure of Paris was proposed , becoming known as the Thiers wall after its chief proponent , prime minister Adolphe Thiers . The plan involved the construction of a new fortified wall around an expanded Paris , the Thiers wall proper , and the building of sixteen new forts a few kilometers farther out . The Fort de Charenton was planned as part of this system . Presently occupied by the National Police , the fort saw passing regiments as well as foreign occupation forces at the time of the Franco - Prussian War of 1870 and the Second World War . History of the Thiers Wall . Before the Napoleonic Wars , Paris had not been invaded by an enemy army since the Hundred Years ' War . Louis - Philippe , proclaimed king of the French in 1830 , was convinced that the key to the defense of France was to prevent Paris from falling too easily into the hands of foreign armies , as in 1814 . He conceived a project to build an enclosure of fortifications around the capital that would make the city impregnable . The first project was presented to the Chambre des Députés at the beginning of 1833 by Marshal Soult , President of the Council and Minister of War . The proposal was sharply opposed by the Left , which suspected , or pretended to suspect , ulterior motives on behalf of the government with respect to internal policy . The Left claimed that the fortifications were actually intended not to defend France , but to threaten Parisians if they revolted against the royal powers . With the walls surrounding Paris a system of 16 detached forts was added , placed a few kilometers away as a first line of defence . Among them was the Fort de Charenton . The Fort de Charenton is a defensive work located in the town of Maisons - Alfort , by whose name it was originally known . It later took the name of the town it was to defend , Charenton - le - Pont . The fort cost 5 million francs at the time , equivalent to 9 million current euros . Construction lasted five years . Choice of location . The fort was originally proposed for the plateau of Charenton - Saint - Maurice , where land was purchased , but the military administration changed its opinion and moved the project to its present site . In the middle of the 19th century , Maisons - Alfort was open country . The hill finally chosen , the Butte de Gramont , had clear lines of fire , apart from the National Veterinary School of Alfort , to the northwest . The is located at a strategic point that was contested in 1814 , where forces under Frederick of Württemberg attacked the bridges of Charenton , defended by veterinary students and some regular troops , and the bridges of Saint - Maur - des - Fossés , obligatory passages on the Marne . The fort commands Route Nationale 6 to Geneva and Route Nationale 19 to Belfort along with the Pont de Charenton on the Marne and the Pont à l ' Anglais on the Seine . Construction . The fort . The fort was built according to the Vauban system . Construction required a site of about 26 hectares , with accompanying difficulties with expropriation from the existing owners . The fort itself occupies an area of approximately 10 hectares with a perimeter of about 1500 metres . The first stone was laid by Louis - Philippe on 19 April 1841 only two weeks after construction was authorized , and the walls were finished the following year . The caserne . Accommodating several hundred men , the fort ' s buildings were laid out in 1843 according to the following program : " The barracks will be laid out to accommodate four companies of approximately 110 men with their warrant officers . . . They will be two stories high above the ground floor and will be composed of a series of bays with a span of 6 . 5 metres , with two windows on each frontage They will be high of two stages above the ground floor , and will be composed d ' a series of spans of 6 , 50 m width , informed by two windows on each façade , and are served two by two , three meters wide and leading directly to the principal façade . Moreover , two other staircases entered at the gable ends are located on each end bay , which are divided into small rooms . The troop quarters are located on the long sides with communicating openings between them . . . they will have a length of 14 . 1 metres and a ceiling height of 3 . 45 metres , and will accommodate twenty - four beds . " " The pitched roof will be zinc - covered with gables at the ends to avoid costs for trusses , on top of the cross walls starting from the attic floor and supported by masonry pillars , on which will rest the roof purlins . Moreover , due to the span of the members , they would otherwise need to be especially heavy , so they have been augmented by bracing that permits a reduction in their dimension to those ordinarily found in commercially available timbers . " " Chimney flues will be installed in the cross walls at each floor that will be offset to meet at a single chimney on the ridge of the building . " " The stairs will be of wood , with one or two additional steps between the ground and first floors compared with the flight between the first and second floors , with sufficient height at the landings to allow access to small rooms behind the stairs . " In 1930 barracks were built outside the fort to accommodate the 3rd cavalry group of the 1st Legion of the Mobile Republican Guard . Ten of these buildings remain along Boulevard Charles de Gaulle . During the German occupation from 1940 , small pillboxes with machine guns were built in the point of each bastion . History . Completed in 1845 , the fort was used as a prison following the Revolution of 1848 . A few years after the rise of Napoleon III the fort ' s armament was updated with rifled guns . The long - range guns had a firing range of 3000 metres . During the Franco - German War the fort took part in the defence of Paris against the Prussians . The fort fired at targets in Moulins - Saquet , the Gare - aux - bœufs , Mont - Mesly , and destroyed part of Choisy - le - Roi , which had been occupied by the Prussians . No fire was returned in the direction of the fort or town . After the Prussian victory , the fort was handed over to occupation troops in February 1871 , and was evacuated in September the same year . In 1910 the garrison was provided by the 1st group of the 59th artillery regiment . By the First World War the garrison was the 3rd regiment of colonial artillery . In 1914 the fort was opccupied by the 32nd divisional regiment , which stayed until the Second World War , when it was sent to the front , and where it was practically destroyed in combat . After the Second World War . Little information is available concerning the German occupation . The fort was used during this time as an ammunition dump and radio transmitting station . As the Allies advanced on Paris , the fort was abandoned by the Germans on 25 August 1944 . Before leaving the Germans set up a timed - detonation device in the hundreds of tons of explosives using an acid - fuse device . The device was defused by bomb disposal expert Roger François and the destruction of the fort and the potential destruction of the town was averted . A plaque commemorates the deed . After 1944 the fort was used by the Gendarmerie and was employed as a center for political prisoners and for juvenile delinquents . The fort was formally transferred to the Gendarmerie in 1950 . It was used as a training and assembly center for units destined to the French war in Indo - China , with more than 6000 gendarmes passing through . After the war , other Gendarmerie units were installed at the fort , with the training command occupying the fort from 1959 to 2000 . The Groupe d ' Intervention de la Gendarmerie Nationale ( GIGN ) was established in 1974 and housed at the Fort de Charenton until 1983 , when it moved to Satory . Presently the fort is occupied by various services of the directorate of the Police Nationale and the historical department of the Gendarmerie .