Fort Constantin: A Prussian Outer Work of Koblenz
Site at a Glance
- Rating
- 4.5
- Popularity
- Low
- Country
- Germany
- Primary era
- Modern
- External website
- Open
- Eras represented
- Medieval, Early Modern, Modern
- Civilizations
- German, Kingdom of Prussia
- Site type
- Military
- Remains
- Fort
On this page19 sections
History
Fort Constantin is a nineteenth-century Prussian fortress work in Koblenz, Germany, built on the outer spur of the Hunsrück as part of the city’s Alexander system. Positioned about 110 metres above sea level southwest of the city centre, it protected the Karthäuser Plateau and its steep approaches toward the Rhine and Moselle. Its construction transformed a former Carthusian monastery into a major element of Koblenz’s defensive landscape.
Monastery and Prussian acquisition
The site may have been inhabited as early as the ninth century. In later centuries it was occupied by a Carthusian monastery, belonging to the Charterhouse order, a Catholic community known for its highly contemplative religious life. By the early nineteenth century, the complex included eight buildings and the associated Berghof estate.
On 23 June 1818, the Prussian state purchased the former monastery, the estate, and their land from the merchant Christian Seidensticker. The transaction cost 47,222 thalers, equivalent to 85,000 Rhenish gulden. From the summer of 1816, before the purchase was completed, the monastery had already been used as barracks for pioneer units engaged in work on nearby Feste Kaiser Alexander, a major Prussian fortress work in Koblenz’s Alexander system.
Parts of the monastery were demolished at the end of 1821 to clear space for a new fort. Construction began with the casemated corps in 1822, followed by the foundations of the gorge tower in 1823. A casemate was a fortified vaulted chamber intended for troops, equipment, or artillery. Most of the remaining monastic buildings were removed in 1824, while the priory building survived temporarily.
Construction and military use
During a visit on 12 September 1825, King Friedrich Wilhelm III of Prussia named the fort for the visiting Russian Grand Duke Konstantin Pavlovich. The main construction was largely finished by 1827. The last remaining priory building was demolished in 1828 and replaced on its foundations by a wartime bakery.
Heinrich Ferdinand Schuberth served as the principal project engineer. Other engineers involved in the work included August Wilhelm Beyse, Friedrich Peter Favreau, Ludwig Gärtner, and Johann Wilhelm von Metzen. Colonel Johann Carl Magdalena von Vigny directed construction between 1823 and 1831, with Gärtner serving under him. The underground connection to Feste Kaiser Alexander was begun in 1823 under Gärtner.
The casemated corps was prepared for troop accommodation from 1831, and the gorge tower from 1850. A permanently stationed unit is not evidenced. Until about 1910, the fort was probably used mainly as a regimental store and workshop by units based at Feste Kaiser Alexander. Its activities included gunsmiths’ and tailors’ workshops, while offices of the fortification administration were also housed there. The fort may at times have accommodated the 42-member band of the 4th Garde-Grenadier Regiment, although the regiment’s documented facilities at the site were its store and workshops.
Three barracks were erected beside the approach road in the early 1870s. They were not intended for troop accommodation and were replaced by a single wooden shed in 1878. A second wartime powder magazine was constructed in 1862 and 1863, using an older monastery cellar.
Downgrading and dismantling
In 1886, the entire Koblenz fortress was classified as a second-line fortress. Its condition was to be maintained rather than substantially improved. Fort Constantin was abandoned on 23 January 1900 and formally surrendered as a fortification on 27 January 1903.
Around 1910, a wooden gallery about 2.5 metres wide was installed along the inner facade. It provided additional space for accommodation, workshops, and offices. The fort’s military fabric was soon affected by the wider dismantling of the Koblenz defences after the First World War.
The Allies required the destruction of the city’s fortifications, and an order for the complete demolition of Fort Constantin was issued on 13 February 1922. German dismantling authorities nevertheless secured its preservation because the fort, together with Feste Ehrenbreitstein, strongly influenced the Koblenz skyline. Between April and the end of August that year, the two wartime powder magazines and the bakery were removed, the covered link to Feste Kaiser Alexander was destroyed, the earth covering was stripped from the casemated corps, and the main ditch was filled.
War, emergency housing, and preservation
During the Second World War, the fort was incorporated into Koblenz’s air-raid and command infrastructure. From July 1944, a three-storey shelter with a concrete roof two metres thick was installed in the northern part of the casemated corps. The wooden gallery was probably removed during this work. Several tunnel shelters also served people living nearby and travellers from the main railway station.
On 25 September 1944, Koblenz police president and SA Brigade Leader August Wetter moved his command post into the gorge tower. As the destruction of central Koblenz intensified, the air-raid warning command transferred to the fort’s bunker complex in late November. It remained there until early March 1945.
On 17 March 1945, the 3rd Battalion of the 345th Infantry Regiment, part of the 87th US Infantry Division, attacked the Karthause and Koblenz from the Hunsrück Heights Road and through Moselweiß and Goldgrube. Fort Constantin became a key position in the defence and the location of the last German resistance on the left bank of the Rhine in this sector. After heavy artillery and tank fire, its garrison of five officers and 70 men, commanded by Captain Franz Josef de Weldige-Cremer, surrendered on 19 March.
From soon after the war until March 1972, the fort provided emergency housing for bombed-out and displaced families. The main gate and window openings were later bricked up, and neglect caused the complex to deteriorate. An illegal tyre store in the wartime bakery was destroyed by fire in 1985, followed soon afterward by the burning of the wooden entrance gate.
The gorge tower also had a post-war communications use. From December 1958, it housed a transmitter serving the Goldgrube and Oberwerth districts. During long-term repairs connected with expansion of the B 9 road, cracks in load-bearing elements were filled and ceilings were stabilized with concrete and steel anchors in 1985. The tower received new exterior plaster in 1987.
Renewed conservation and interpretation
The association PRO KONSTANTIN e. V. was founded on 12 September 1993 to arrest the fort’s deterioration and establish a lasting use. The site reopened to the public on 11 September 1994. Initial work secured and cleared the complex, removed rubble from the casemates, cleared vegetation from roof surfaces, and cleaned debris from the former bakery cellars. Entrances were closed and protected against vandalism.
From the mid-1990s, employment-creation measures supported archaeological clearance, structural stabilization, masonry and plaster repairs, and landscape work. Courtyard excavations began in July 1995. In 1997, restoration of the Prussian courtyard level revealed the crypt of the medieval monastery church, the original floor, and substantial remains of the bakery ovens. Repairs to the roof of the casemated building were especially important for protecting its surviving structure.
Exhibitions and events gradually resumed from 1994, and by about 2000 some rooms were permanently usable and guided tours had begun. The gorge tower was adapted as a museum and has housed the Rhenish Carnival Museum, operated by the Koblenz Carnival Working Group, since 2000. PRO KONSTANTIN e. V. manages and develops the rest of the fort. Restoration of windows and exterior doors in the southern wing began in 2005, and the restored, partly reconstructed main gate was reinstalled in November 2007. An arson attack on 5 January 2013 badly damaged the association’s exhibition area. Since 2015, the bunker complex has contained a permanent exhibition on Koblenz during the Second World War.
Fort Constantin is protected as a cultural monument under the monument-protection law of Rhineland-Palatinate and is listed in the state monument register. It also carries the blue-and-white emblem established by the Hague Convention to identify cultural property protected during armed conflict. Since 2002, it has formed part of the UNESCO World Heritage property of the Upper Middle Rhine Valley, a culturally and historically important Rhine landscape containing fortifications, settlements, monuments, and related heritage.
Remains
Fort Constantin is arranged around a three-winged casemated corps and an adjoining courtyard. A northern ramp descends to a lower plateau where the former powder magazine survives through its foundations. A covered passage once led toward the gorge tower, while the wartime bakery occupies the eastern vineyard slope. The north side borders a rocky steep slope containing the air-raid bunker. The fort’s artillery positions covered the Karthäuser Plateau toward the Rhine and Moselle, while guns in the casemated corps protected the rear of Feste Kaiser Alexander.
Casemated corps
Outer defensive structure
The casemated corps is a wall-like, three-winged building with 19 structural axes and two projecting angles facing southwest. Its 18 ground-floor casemates are arranged behind the long defensive facade, whose principal entrance lies in the fifth axis from the north. The openings were originally gun embrasures. After the fortifications were dismantled, they were enlarged into segmental-arched windows, with some still flanked by loopholes.
The lower level contains 12 casemates, three in the northern section and nine in the eastern section. The middle section has no basement, while two additional casemates occupy a second basement level at the building’s ends. Barrel vaults cover the chambers, which are linked by passages with basket-shaped arches. Rectangular openings in two vaults served cannon lifts, and semicircular niches in the walls held stoves.
On the side facing the glacis, the building was protected by a masonry dry ditch. Only its southeastern section survives, and the Rhine-side ditch defence has been exposed. Three ditch-defence works protected the structure. The casemates were not intended for permanent peacetime occupation, apart from two specially insulated guard chambers beside the main entrance. Deep grooves in the outer walls could hold a timber barrier designed to provide protection from gunfire.
Courtyard facade and wartime bunker
The courtyard facade is more elaborate than the outer side. Semicircular stair towers project from the two angles and rise a complete round storey above the casemates. Narrow openings in the towers resemble loopholes, and each is capped by a shallow conical roof. The casemates have round-arched doors, paired rectangular windows, and a tall simplified entablature. Cube-shaped structures at the ends contain staircases.
Four stairwells and the lower entablature zone between the round towers end in pointed-arched decorative arcades. A northern casemate was converted into a strongly built Second World War bunker while retaining much of the earlier structure. The rectangular bunker incorporates parts of the northern terrace and has an external brick facing.
Main entrance
Gate complex
The representative main entrance was formed as a gate complex with an inner covered passage. Its unusually elaborate outer facade differed from the generally plain enemy-facing sides of contemporary Koblenz fortress gates. A pitched roof covered the gate, and a one-storey blockhouse occupied its centre. Windows in the side walls, a rear entrance, and an outer round-arched portal indicate that the blockhouse probably served mainly as an observation post. Semicircular stove recesses were built into its side walls.
The gable contained a blind arch with an inscription and a cast-iron, possibly bronze-coated Prussian eagle. Both were reconstructed in 2012 and 2013. Three tall rectangular loopholes below the inscription covered the approach with small arms. Their rounded connected surrounds were made from red Miltenberg sandstone. Another loophole form, resembling medieval machicolations, was probably chiefly decorative and is unusual in Prussian fortification architecture.
Bridge and interior passage
A drawbridge formerly crossed the ditch before the entrance. An earth causeway replaced it in 1887. The cellar beneath the vestibule held the drawbridge counterweights, and restoration exposed the room and made it accessible again. Inside the gate were a guardroom and detention cell, while the gate hall led into the casemates. The entrance area was altered repeatedly, especially after 1910 and during its Second World War conversion for air-raid use, but remained the fort’s central access point.
Underground connection
A covered underground passage to Feste Kaiser Alexander began in 1823. It started in the basement of the central casemated section, at Casemate 10, and extended horizontally beneath the ground through the ditch defence toward the area of present-day Simmerer Straße. A staircase of 205 steps crossed the change in elevation toward the area of present-day Hüberlingsweg, after which the passage continued underground to Casemate 7, the gorge redoubt of Feste Kaiser Alexander.
The passage was about two metres wide, barrel-vaulted, and covered with earth on its slope side. Thirty-five loopholes ran along the uphill side. Freshwater and wastewater pipes passed through it, and from 1859 an electric cable linked the telegraph in the redoubt with the central station in the city. The connection was destroyed during the 1922 dismantling of the fortifications.
Courtyard and service structures
Ramps, paving, and monastery crypt
A curved artillery ramp in the courtyard descends toward the fifth casemate from the east. Numerous stretches of original Prussian paving remain beside the casemated corps. The crypt of the medieval monastery church, uncovered in front of the wartime bakery, is visible in the courtyard. A ramp for wheeled vehicles reaches the lower northern courtyard, which connects with the former covered way and a substantial basalt staircase leading to the gorge tower. An approach from Koblenz’s former Way of the Cross to the Carthusian monastery probably existed here from the fifteenth century.
Water supply and powder magazine
The powder magazine beneath the courtyard was demolished during the dismantling of the fortifications, leaving its foundations as the visible remains. In the western courtyard, a circular opening marks a cistern measuring about eight by five metres. It was connected to the well cistern in the redoubt of Feste Kaiser Alexander, linked to a well inside Spitzberg Barracks in 1884, and later connected to an underground elevated reservoir at Löwentor.
Wartime bakery
The wartime bakery stands on the eastern side of the courtyard. It was probably built by 1830 from the remains of the Carthusian priory, which had been constructed between 1720 and 1737 and reduced to half the height of its ground floor in 1828. The structure also served as a gun platform. Its storage rooms included a large hall with two substantial ovens, and its cellar spaces were reached by a long, straight staircase from the courtyard.
The ovens stood on masonry platforms. The baking hall had a barrel vault with lunettes corresponding to windows on the valley side, where the structure has collapsed. Like other wartime bakeries in the Koblenz fortress, it provided bombproof shelter. Four buttresses were added to the outer eastern wall around 1900 and rose above the baking-room windows.
The ovens were destroyed during the 1922 dismantling. Each measured about 4.3 metres long and 3.7 metres wide, with an estimated capacity of 250 loaves per baking cycle. At maximum output, the bakery could have produced approximately 2,000 loaves a day. Remains of a boiler for baking water stand beside the northern oven position, and the hall is paved with Bunter sandstone slabs.
Two square corner turrets with loopholes and pyramid roofs form the upper end of the eastern structure. A crenellated wall joins them. Two ramps for wheeled vehicles approach the building from the west. In the southern wall, two round-arched doors lead to latrines, regarded as an early nineteenth-century hygienic innovation in Prussian fortress construction.
Gorge tower
The gorge tower, a defensive tower placed at the rear of a fort, is the most visible part of Fort Constantin from the city. A covered way once led from the lower courtyard across a bridge that no longer survives to the tower’s upper storey. The tower rests against the rock on an irregular plan rounded toward the southeast and has a very deep basement.
Its rounded valley facade rises through three storeys and ends in a terrace with a crenellated parapet. The straight uphill side begins at ground-floor level at the main entrance and culminates in a pentagonal blockhouse with large lunette windows and a shallow tent roof. The blockhouse received the entrance from the covered way.
Rifle loopholes pierce the basement. The ground and upper storeys originally held cannon embrasures, later enlarged into segmental-arched windows during the dismantling of the fortifications. Smoke-vent openings lie above them. Cornice bands separate the storeys, and the entrance has a rectangular surround of red sandstone. The outer walls and storeys are two metres thick.
A spiral staircase beside the main entrance leads to the blockhouse. Inside, the vaults rest on a central seven-sided pier. A gun lift allowed artillery to be moved from the ground floor to the blockhouse.
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