a former Kreis (administrative district) and state of Germany, between Westphalia and Hesse-Nassau. For centuries a principality and from November 1918 to March 1929 a republic and constituent state of the Weimar Republic, it was on April 1, 1929, amalgamated with Prussia at the request of its people. It had an area of 420 square miles (1,088 square km), covered with hills containing farmland, mines, and slate and stone quarries. The old capital was Arolsen.