Königstein Fortress, one of the largest mountain fortresses in Europe, rises high in the Elbe Sandstone Mountains of Saxon Switzerland. The "Burgrave Gebhard vom Stein" is first mentioned in a document of King Wenceslas I of Bohemia in 1233, presumably referring to Königstein. At that time the area belonged to the Kingdom of Bohemia. In the 16th century, the castle underwent significant expansion to become a Saxon state fortress, with the start of construction of the imposing 152.5-metre-deep castle well between 1566 and 1569 being an important milestone. It is still one of the deepest historic wells in Germany.