The Margraviate lay east of Bohemia proper, with an area about half that region's size. In the north, the Sudeten Mountains, which extend to the Moravian Gate, formed the border with the Polish Duchy of Silesia, incorporated as a Bohemian crown land upon the 1335 Treaty of Trentschin. In the east and southeast, the western Carpathian Mountains separated it from present-day Slovakia. In the south, the winding Thaya River marked the border with the Duchy of Austria.