TANNENBERG, BATTLE OF

also called Battle of Grnfelde, or Grunwald (July 15, 1410), battle fought at Tannenberg (Polish: Stebark) in northeastern Poland (formerly East Prussia) that was a major Polish-Lithuanian victory over the Knights of the Teutonic Order. The battle marked the end of the order's expansion along the southeastern coast of the Baltic Sea and the beginning of the decline of its power. Polish and Lithuanian forces proceeding toward the order's stronghold, Marienburg, met its army between the villages of Grnfelde (Polish: Grunwald) and Tannenberg. Though the order defeated the Lithuanian contingent, the ranks of the Poles remained unbroken. By the end of the 10-hour battle, the order's forces had been crushed and its grand master, most of its commanders, and 205 of its knights had been killed. Subsequently many Prussian castles controlled by the order surrendered to the Polish-Lithuanian force, though Marienburg, which was defended by Heinrich Reuss von Plauen, did not fall. By September 1410 the Polish-Lithuanian army withdrew. (Aug. 2630, 1914), battle fought at Tannenberg (Polish: Stebark), in what is now northeastern Poland, that ended in a German victory over the Russians in the early days of World War I. Two Russian armies, the 1st, which was under General P.K. Rennenkampf, and the 2nd, under A.V. Samsonov, invaded German East Prussia in August 1914. Rennenkampf fought a successful action at Gumbinnen on August 20 but failed to maintain contact with Samsonov. The German commanders Paul von Hindenburg and Erich Ludendorff, making use of a plan devised by Lieutenant Colonel Max Hoffmann, threw all their strength against Samsonov's isolated army near Uzdowo, just south of the historic site of Tannenberg (August 26). Samsonov fell back, losing about half of his army in the next few days, and the Germans took 92,000 prisoners. Samsonov shot himself in despair on August 29. The Russians lost another 30,000 killed or wounded, while the Germans sustained a total of 13,000 casualties. Tannenberg was a crushing defeat for Russia, which lost almost an entire army, 400 cannons, and other war matriel. The Russians' premature invasion of East Prussia had, however, compelled the Germans to divert troops from their attack on France at a crucial moment of that campaign.