Marchfeld (märkhˈfĕltˌ) [key], plain, NE Austria, NE of Vienna, between the Danube and the Morava (Ger. March ) rivers, on the border of Slovakia. A strategic approach to Vienna, it was the site of several important battles. In 1260, Ottocar II of Bohemia defeated Bela IV of Hungary on the Marchfeld, and in 1278, Ottocar was defeated and slain by the forces of Rudolf I of the house of Hapsburg. In 1809, Napoleon I was defeated on the Marchfeld at Aspern by Archduke Charles, but was victorious at Wagram.