Poznań Fortress: Prussian Fortifications in Poland
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History
Poznań Fortress is a Prussian system of fortifications in Poznań, Poland, constructed from the nineteenth century into the early twentieth century. It combined a polygonal inner fortress around the historic city with an outer ring of forts and supporting installations. The complex protected Poznań after the city came under Prussian rule in 1793 and was also intended to strengthen the defence of Berlin against a possible advance from the Russian-controlled east.
Planning and construction
Poznań’s medieval walls had become largely obsolete and were mostly removed in the early nineteenth century. New Prussian plans began in December 1815 because the city stood on the shortest route from the Prussian-Russian frontier towards Berlin, as well as on the route linking West Prussia with Silesia. General Karl von Grolman, a senior Prussian commander and former Chief of the Prussian General Staff, became the principal early advocate of a modern fortress.
Grolman’s preliminary plan of 9 July 1817 focused on Winiary Hill and the area around the Reformed church and monastery. Military engineers later incorporated the Warta and Wierzbak rivers into the defensive system by adding weirs, structures that controlled water levels and could assist fortification. Construction planned for 1817 was delayed until 1828 while funds were directed to the fortresses of Cologne and Koblenz.
In 1823, Grolman proposed a continuous defensive line around the left-bank city, supported by works placed 500 to 1,000 metres in front of it. Johann von Brese prepared the detailed plan dated 23 March 1828. It included the main fort on Winiary Hill, works on Ostrów Tumski and the Warta’s right bank, and a continuous fortified boundary, or enceinte, around the left-bank city. General Gustav von Rauch approved the revised plan, and King Frederick William III gave final approval on 14 August 1828.
Captain Moritz von Prittwitz und Gaffron became chief of construction on 14 March 1828. Work began on 23 June with the defensive barracks of the Winiary fort. The 5th Pioneer Detachment moved from Glogau to Poznań, although shortages of money slowed progress. During the November Uprising of 1830 to 1831, a Polish revolt against Russian rule, the unfinished fortress was temporarily prepared for defence and manned.
The inner fortress
Fort Winiary was completed in 1839. Its central defensive barracks, known as the Kernwerk, were finished in 1832, while the first redoubts, or enclosed defensive works, were completed by 1830. Its outer front, flanks, gorge, and later ravelins, which were detached works placed before the main defensive line, followed during the 1830s. In 1834 the fortress became a Prussian Fortress Second Class, and its completed works were armed and occupied. General Hoffman became its first commandant.
Water-control works formed an important part of the early system. The Great Lock on the Warta was built in 1829 to 1832, and the river’s main course was moved westward in October 1832. The Little Lock on the Wierzbak followed between 1832 and 1837. The Cathedral Lock and related works on Ostrów Tumski were constructed from 1834 to 1838, and further works made the cathedral island independently defensible from about 1850.
Work on the left-bank enceinte resumed in March 1840 under Reichel and later continued under Lange. Bastions III and V were built first, followed by Bastions IV, VI, II, and I. Construction was interrupted in 1848 by the Greater Poland Uprising and the wider European revolutions known as the Springtime of Nations. Connecting covered ways, an internal rampart road, and numerous brick blockhouses were added in 1860 and 1861.
The right-bank defences developed from 1835. The northern connecting rampart and Bydgoszcz Gate were completed in 1839, Fort Reformatów in 1842, and the Warsaw Gate, Cybina Cavalier, Cybina Lock, Fort Rochus, and related works during the 1840s. Ostrów Tumski received flood-control canals, Dom Redoute, eastern and western bridgeheads, and Dom Lünette. The moat of Dom Redoute was completed around 1862.
The polygonal fortress was declared complete and classified as a Fortress First Class in 1864. King Wilhelm I then renamed many works after Prussian generals. Fort Winiary’s bastions became Bastions Johann, Leopold, and Ludwig, while the left-bank cavaliers and bastions received names including Boyen, Röder, Witzleben, Brünneck, Rohr, Grolman, Strotha, Colomb, Stockhausen, Tietzen, Bonin, and Waldersee.
The outer ring
Improved artillery, new explosives, railways, tramways, and changes to the hydraulic system forced repeated modifications from the 1860s to about 1910. Powder magazines were strengthened, laboratories and artillery positions were added, and bridges and gates were modernized. The Berlin Gate was adapted for tram traffic in 1880, while railway gates and new access routes altered the fortress’s connections with the growing city.
The Crimean War and the Danish War of 1864 showed that compact polygonal fortresses were vulnerable to rifled artillery and elongated explosive shells. Prussian planners therefore adopted an outer ring of forts several kilometres from the older enceinte, reducing the military importance of the inner line. Poznań was selected for major modernization under imperial decisions made between 1871 and 1874. The final plan, approved on 24 February 1876, followed the system developed by Hans Alexis von Biehler.
The plan provided for nine main forts and three intermediate forts. More than seven million thalers were assigned to land, construction, and artillery, and French prisoners of war were used as labour. Construction began in 1876. The ring reached approximately 9.5 kilometres in diameter and about 30 kilometres in defensive length, generally lying 2 to 4.5 kilometres beyond the inner fortress. Roads linked the forts to one another and to the city, including a circular road behind the forts and radial routes.
New explosive shells and melinite led to a second modernization phase from 1887. Six newer intermediate forts, numbered Ia, IIa, IIIa, Va, VIIa, and VIIIa, were added, probably between 1890 and 1896. An intermediate fort now stood between successive main forts. The system also acquired the permanent Bogdanka Battery, 43 infantry, artillery, and ammunition shelters, a Cybina weir, a peacetime powder store, additional firing ranges, and modernized main forts.
By 1900 Poznań again belonged to the highest category of large fortresses. Work completed around 1907 added ten infantry shelters, three artillery shelters, three ammunition shelters, artillery observation positions, and additional ammunition storage. A proposed outer ring with a radius of about 50 kilometres was abandoned in 1913, but more than one hundred passive shelters were built behind the existing forts.
Demolition and Polish control
The outer ring made the polygonal fortress militarily redundant and restricted urban growth. Mayor Richard Witting began seeking its removal in 1891. After negotiations over the value of the fortress land, the central government paid the army, while the land remained state property. Emperor Wilhelm II confirmed demolition of the left-bank enceinte on 3 September 1902. Demolition had already begun and continued until 1912.
Most of the left-bank enceinte was removed, although Fort Winiary, works on Ostrów Tumski and the right bank, the redoubt of Bastion III Grolman, and a blockhouse connected with Bastion IV Colomb survived at that stage. The names of the demolished works were transferred to outer forts, including Fort I Röder, Fort Ia Boyen, Fort IV Hake, Fort V Waldersee I, Fort Va Bonin, Fort VII Colomb, Fort VIII Grolman, Fort VIIIa Rohr, Fort IX Brünneck, and Fort IXa Witzleben.
During the Wielkopolska Uprising of 1918 to 1919, German troops generally stayed in barracks or forts. Polish forces took many of the fortifications through negotiation, sometimes after exchanges of fire or brief fighting. After Poznań came under Polish control, the fortress was used by Polish military and communications units.
Polish authorities resumed demolition after the First World War. The Great Lock and Cathedral Lock began to be demolished in 1919, parts of the right-bank works were levelled in 1920, and general demolition of the inner fortifications was approved in 1923. Most of this work took place between 1924 and 1927, including the removal of the Warsaw and Bydgoszcz Gates and the ramparts of the former Redutas Radziwiłła, Lecha, Reformatów, Rusa, Czecha, and Saint Roch.
War, occupation, and later change
The surviving Fort Winiary, several gun emplacements, Reduta Czecha, and Kalisz Gate formed part of the interwar remains. The outer forts continued to influence Polish defence planning, although they were not maintained in combat readiness. Some served as military stores, while unattended forts were used locally for storage or housing. The system was then known as the Poznań Fortified Camp.
During the German occupation, Fort VII operated as a concentration camp from October 1939 to April 1944. It became a site of mass murder of Polish prisoners, and up to 20,000 Poles died there through execution, torture, and harsh conditions. Forts Grolman and Rauch also formed the nucleus of the Stalag XXI-D prisoner-of-war camp.
In the final phase of the Second World War, the German authorities declared Poznań a fortress to be defended at all costs. The outer forts contributed to the city’s defence during the Battle of Poznań in 1945, while Fort Winiary became the final major point of resistance. The fortress fell on 23 February 1945 after a five-day siege in which several thousand soldiers and defenders were killed.
Fort Winiary was severely damaged after the war and was converted during the 1950s into Cytadela Park. The outer forts remained in varied condition and acquired military, industrial, storage, museum, memorial, and other uses. Most are now owned by the city or occupied by private organizations and companies.
Remains
The inner fortress and water defences
The original system was organized around a polygonal inner fortress enclosing the historic centre, with additional works on the Warta’s right bank and on Ostrów Tumski. The six left-bank bastions, linked by curtains, cavaliers, covered ways, and blockhouses, formed the principal urban defence. A caponier, a protected work projecting into a ditch for fire along its sides, protected each bastion. The Grobla caponier stood separately on what was then an island.
Fort Winiary
Fort Winiary occupied Winiary Hill north of the historic city and covered about 100 hectares. Its Kernwerk was a central defensive barracks and final strongpoint, surrounded by a polygonal rampart, dry ditches, three bastions, four projecting ravelins, and four independent redoubts. Separate artillery and infantry bridges, observation towers, gun positions, magazines, and water-control works formed part of the complex. The dry ditch was reported as 6 to 32 metres wide and about 7 metres deep, while the building walls were approximately 1.3 to 1.8 metres thick. Substantial elements survive within Cytadela Park.
Great and Little Locks
The Great Lock on the Warta served as both a weir and a bridge, linking Fort Winiary with the eastern bridgehead later called Fort Roon. Its ship passages were widened in 1888 for larger vessels. After demolition, parts of its bridgeheads remained. The Little Lock on the Wierzbak linked the western end of Fort Winiary with Fort Adalbert, later Fort Hake. The stream was later combined with the Bogdanka and carried partly through underground drainage channels.
Left-bank bastions and gates
Bastion I and Cavalier Boyen contained the Grobla Lock, also called the Grabendamm, an overflow weir that regulated water levels in a former Warta branch and in the moat. The blockhouse of Bastion Colomb survives and was excavated and restored in 1998. Other surviving inner-fortress elements include part of the reduit of Fort Roon at the Garbary cogeneration plant, the railway caponier near the Poznań rapid-transit line, and fragments of other redoubts and ramparts.
The inner fortress included Szelągowska Gate by the Great Lock, Cemetery Gate by the Little Lock, Mill Gate near Fort Hake, and Bydgoszcz Gate by the Cathedral Lock. Later entrances included Wilda, Berlin, Warsaw, Warta, Royal, Grobla, Dębina, and Kalisz Gates, together with a railway gate near Bastion IV and Knight’s Gate in Cavalier Strotha. Berlin Gate was built from 1843 to 1850, widened in 1867 to 1869, and adapted for trams in 1880. Cemetery Gate was replaced by a railway blockhouse in 1889 to 1894.
Right-bank and cathedral-island works
Fort Hake and Fort Prittwitz-Gaffron
Fort Adalbert, later Fort Hake, stood north of the hill containing Saint Adalbert’s Church. The Magazin Cavalier formed a fortified embankment south of the fort, while the Brick Lunette, later Waldersee Lunette, connected with the defensive line through a long gorge. The form and position of the former Fort Hake redoubt are reflected by the Collegium Da Vinci building.
Fort Reformatów stood on a hill beside the former Reformed monastery and the Church of Saint Casimir in Śródka. Its lower reduit survives. Fort Rauch had a western riverbank caponier, and its gun emplacements survived the interwar demolitions. The fort later became Fort Prittwitz-Gaffron and Reduta Reformatów in the changing nomenclature of the site.
Ostrów Tumski
The fortifications of Ostrów Tumski included the Cathedral Lock, North Cathedral Cavalier, Dom Lünette, Dom Redoute, and Dom Flesche, later Fort Steinäcker. Eastern and western flood-control canals surrounded the island. Dom Redoute had a five-sided plan and a moat completed around 1862. A powder magazine holding up to 51 tonnes was added to the North Cathedral Cavalier in 1861.
The Cathedral Lock was demolished after the First World War, but its western bridgehead survives. Between 2011 and 2014 it served as the bridgehead of a footbridge leading to the Brama Poznania cultural centre. Dom Flesche, later Fort Steinäcker and Reduta Lecha, stood north of the cathedral. An earthwork built in front of it in 1836 protected the lunette and an access road. Changes to the Cybina in the early 1870s placed the fort on Ostrów Tumski, and it was reinforced in 1910.
The outer forts
The outer ring consisted of nine main forts, three older intermediate forts, six newer intermediate forts, batteries, shelters, ammunition stores, roads, firing ranges, and training grounds. The main forts stood at intervals of roughly 3 to 4 kilometres, generally 2 to 4.5 kilometres beyond the inner fortress. Intermediate forts covered gaps created by the Bogdanka and Warta valleys. Three permanent artillery batteries were planned to support Fort III.
The main forts were numbered I to IX. The older intermediate forts were IVa, VIa, and IXa, while the later group comprised Ia, IIa, IIIa, Va, VIIa, and VIIIa. The principal forts were constructed between 1876 and 1883, with Fort V completed in 1886. The outer works used two main forms, artillery forts and intermediate positions. Later designs distributed artillery more widely and relied increasingly on protected infantry positions, shelters, concealed roads, and ammunition stores.
Forts I to III
Fort I was built from 1878 to 1880 and is partly used for storage. Part of its ditch was roofed during the Second World War. Fort Ia is unused, with a flooded ditch and lost metal fittings. Fort II, constructed from 1878 to 1882, is used for storage, and part of its ditch was also roofed during the war.
Fort IIa is partly renovated and used by the Salamandra association. Its ditch is flooded, and revitalization has proceeded gradually. Fort III, built from 1877 to 1881, has been under the care of the Poznań Association of Fortress Enthusiasts since 2011. Sections of its barracks vaults were removed in the 1970s and 1980s.
Forts IIIa to V
Fort IIIa was renovated and altered with an added corridor and front entrance. It is used as a crematorium, and its steel shutters survive. Fort IV was blown up, leaving difficult-to-find remains. Fort IVa was also blown up, but part of its main postern and some underground rooms survive. Fort V was destroyed by explosion, although its outline geometry and scattered remains can still be traced.
Fort Va survives in good condition and is opened by the Kernwerk Fortress Enthusiasts Association. Fort V’s location among housing estates has been associated with fatal accidents during attempted exploration. The remains of Fort IVa are occasionally opened by a local fortress and exploration group.
Forts VI to VIIIa
Fort VI survives in very good condition and is occasionally opened. Fort VIa was blown up, leaving limited barracks-room remains and counterscarp walls. Fort VII survives in good condition and contains the Museum of Wielkopolska Martyrdom, recalling its use as a concentration camp during the Second World War.
Fort VIIa remains in good condition but is privately owned and inaccessible. Fort VIII is also in good condition and privately owned. Fort VIIIa survives in good condition, although part of its ditch flooded after damage to the drainage system. A fire damaged the fort in 2006, and part of the building is used by a private service and commercial company.
Forts IX and IXa
Fort IX survives, although its left battery was demolished during the second half of the twentieth century. Fort IXa is the most complete of the older intermediate forts. Its right flank was removed, and part of its ditch was eliminated in 1942 for railway line 271. Another section of the ditch remains flooded, and the fort is used for paintball activities.
Traces within the modern city
The outline of the former Grolman to Waldersee sector remains visible from above and on maps through a pattern of broad green areas and streets. A sculpture of the Archangel Michael from Dębina Gate was placed on a school façade. Other surviving traces include remains of the Cybina Lock beneath Jana Pawła II Avenue, parts of the Great Lock bridgeheads, the Cathedral Lock bridgehead, and fragments of former redoubts and ramparts. Together with the outer forts, these remains preserve the changing scale and design of Poznań Fortress from its first polygonal lines to its dispersed modern ring.
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