The Duchies of Silesia were a crown land of the Bohemian Crown, that were formed when Duchy of Silesia joined the Kingdom of Bohemia in 1335 under the Treaty of Trentschin. The duchies were ruled by the Dukes of Silesia, consisted of the Duchy of Lower Silesia, the Duchy of Upper Silesia and numerous other duchies. A part of the Silesian territory seceded to Kingdom of Prussia as the Province of Silesia in 1815; and the Duchy of Teschen, Duchy of Troppau and Duchy of Nysa remained under control of the Bohemian crown lands as Austrian Silesia until 1918.