I
(August 26–30, 1914) Battle in World War I between Germany and Russia in modern northeastern Poland.
Two Russian armies invaded German East Prussia but became separated. German forces under
II
(July 15, 1410) Major Polish-Lithuanian victory over the Knights of the {{link=Teutonic Order">Teutonic Order .
Fought near the villages of Grünfelde and Tannenberg in northeastern Poland (formerly East Prussia), 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.