Tannenberg, Pol. Stębark, village, Warmińsko-Mazurskie prov., NE Poland, near Olsztyn. Formerly in East Prussia, it was transferred (1945) by the Potsdam Conference to Polish administration. Two important battles were fought there. In the first, fought in 1410 between Tannenberg and the nearby village of Grünwald, Polish and Lithuanian forces under Ladislaus II (Ladislaus Jagiello) halted the eastward expansion of the Teutonic Knights. The second and better-known battle occurred during World War I (Aug. 27-30, 1914). Russian armies under generals Samsonov and Rennenkampf had invaded East Prussia from the south and east, respectively. German strategy was to surround Samsonov's forces; 90,000 Russian prisoners were taken, and Samsonov committed suicide. Rennenkampf, whose unwillingness to aid Samsonov greatly facilitated the German victory, was defeated soon afterward in the battle of the Masurian Lakes. The Russian advance into East Prussia, though ill-fated, relieved considerably the German pressure against the West during the first critical weeks of the war. The battle of Tannenberg is a central event in Aleksandr Solzhenitsyn's novel August 1914 (1972).