Moravia borders Bohemia in the west, Lower Austria in the south(west), Slovakia in the southeast, Poland very shortly in the north, and Czech Silesia in the northeast. Its natural boundary is formed by the Sudetes mountains in the north, the Carpathians in the east and the Bohemian-Moravian Highlands in the west (the border runs from Králický Sněžník in the north, over Suchý vrch, across Upper Svratka Highlands and Javořice Highlands to tripoint nearby Slavonice in the south). The Thaya river meanders along the border with Austria and the tripoint of Moravia, Austria and Slovakia is at the confluence of the Thaya and Morava rivers. The northeast border with Silesia runs partly along the Moravice, Oder and Ostravice rivers. Between 1782 and 1850, Moravia (also thus known as "Moravia-Silesia") also included a small portion of the former province of Silesia – the Austrian Silesia (when Frederick the Great annexed most of ancient Silesia (the land of upper and middle Oder river) to Prussia, Silesia's southernmost part remained with the Habsburgs).