Poznań Fortress, known in German as Festung Posen (Polish: Twierdza Poznań) was a set of fortifications in the city of Poznań (German: Posen) in western Poland, built under Prussian rule in the 19th and early 20th centuries. It represents the third largest system of its kind in Europe.
The first set of fortifications was a tight defensive ring around central Poznań, including the main citadel called Fort Winiary (now the Cytadela park). Construction of these fortifications began in 1828. Later, beginning in 1876, an outer defensive ring was built around the perimeter of the city, consisting chiefly of a series of "forts", which mostly still survive.
The term Festung Posen was also used by the Nazi German occupiers during the Red Army's advance in the closing phases of the Second World War, to refer to Poznań's status as one of the "strongholds" (Festungen) which were to be defended at all costs. It fell in the Battle of Poznań (1945), with Fort Winiary the last point of resistance.
Initial planning
Poznań (Posen) came under Prussian rule with the Second Partition of Poland in 1793. Its medieval city walls were obsolete by that time, and were mostly taken down in the early 19th century to facilitate the city's growth. The Prussian authorities first made plans to build new fortifications in December 1815. The city lay on the shortest route from the border with Congress Poland (and hence with the Russian Empire) to Berlin, and was also an important point on the route from West Prussia to Silesia; therefore, according to General Karl von Grolman, its fortification would show that Prussia had no intention of giving up those lands, and would defeat the "continuous intrigues and plotting" on the part of the Poles. A preliminary plan sketched by Grolman on 9 July 1817 provided for fortification of Winiary Hill north of the city, as well as the area of St. Kazimierz's Church in Śródka to the east. Army engineers added to these plans a weir on the river Warta (Warthe), which would enable the river to be used as part of the defences.
Building was planned to begin in 1817, but initially no funds were available for the work (due to the costs of fortifying Cologne and Koblenz). Planning continued, however: in 1823 Grolman proposed a line of defences surrounding the left-bank (main) portion of the city, with additional fortifications 500–1000 metres in front of the main line.
In 1827, Johann von Brese, then working in the War Ministry's engineering section, was instructed to prepare a detailed plan. The result, dated 23 March 1828, included the large fort on Winiary Hill, fortifications on the cathedral island (Ostrów Tumski) and the right bank, and the core defensive line surrounding the left-bank city. The plan was approved by General Gustav von Rauch (chief inspector of forts), and then presented by General Karl von Hake to King Frederick William III, who approved it in principle, asking Rauch to make some improvements. These were agreed on 18 June 1828 by a committee of officers headed by Rauch, and then supplemented by Rauch himself (it was due to Rauch that Grolman's proposed additional line in front of the main defences was excluded from the plans). The king gave his final approval on 14 August 1828, ordering Hake to begin construction with the Winiary fort and the weirs on the Warta and on the Wierzbak (Wierzbach) stream.
Construction of the inner fortifications
On 14 March 1828 Captain Moritz von Prittwitz und Gaffron, who had been a member of Rauch's committee, was appointed chief of construction of Festung Posen. In May, he and five subordinate officers began marking out the outline of the first fortifications – the defensive barracks of the Winiary fort (later the reduit). Building began on 23 June 1828 (the fort would be completed in 1839). Fortification also soon began north of Poznań Cathedral and in the south-western part of the main defensive line. Work was carried out by the 5th Pioneers Division, re-stationed from Glogau (Głogów). Following the Polish November Uprising against Russia in 1830, the unfinished fortifications were manned temporarily for defensive purposes.