The defenders were somewhat aided by fortifications from previous eras, including a major Imperial Russian-era fortress complex at Osowiec on the Biebrza River that was a scene of a siege in 1915 (February to August) during the First World War, and which was partly demolished by Wehrmacht troops in 1939 before its surrender to the Red Army.
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Osovets is the Russianised version of the Polish name Osowiec / Ossowiec / Ossowitz.
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