Second Battle (February-March 1915) Īttempting to cut the railway line between Białystok and Warsaw, the Germans attacked the Osowiec fortress, which was lightly defended by a few Russian battalions. The day afterwards, two Russian flanking counter-attacks forced German artillery to relocate, taking the fortress outside of German artillery range. Two days later, a German frontal assault was repelled by Russian artillery. By 21 September, the German advance brought the fortress proper within range of German artillery further reinforced with 60 additional guns of calibres up to 203mm, but these could only be brought into action on 26 September. In September 1914, Russian field defenses surrounding the fortress were attacked by 40 infantry battalions of the German 8th Army the attackers enjoyed significant numerical superiority. Other parts of the fortress still belong to the Polish Army and access is restricted.įirst World War First German Assault (September 1914) The visitor information center of the park is located in Osowiec-Twierdza, a small settlement located within the boundaries of the fortress. Today, some parts of the fortress are accessible to tourists, especially the parts within the boundaries of Biebrza National Park. During the German invasion of Poland in 1939 it was bypassed and did not see much fighting.

In the interwar years the fortress was used by the Polish Army. The fortress saw heavy fighting during the beginning of World War I in the eastern front from September 1914 until the Russian Army abandoned it in August 1915. The strategic Belostok– Lyck– Königsberg rail line also ran through the fortress and crossed the Biebrza river there. The extensive marshlands and bogs that surrounded it made attacks upon it difficult. It was located on the river Biebrza about 50 km from the border with the German province of East Prussia, in the one place where the marshlands of the river could be crossed, hence controlling a vital chokepoint. In 1889–1893, military engineer Nestor Buinitsky took an important part in the creation of the fortress. The fortress was built in the years 1882–1892 as one of the defensive works to protect the western borders of Russia against Germany, and continuously modernised afterwards to cope with advances in heavy siege artillery. It saw heavy fighting during World War I when it was defended for several months by its Russian garrison against German attacks. Osowiec Fortress ( Polish: Twierdza Osowiec, Russian: Крепость Осовец) is a 19th-century fortress built by the Russian Empire, located in what is now north-eastern Poland.

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