Hohentwiel -The fortress, whose ruins lie on top of Hohentwiel, was constructed in 914 using stone taken from the mountain itself by Burchard III, Duke of Swabia. Originally, the Monastery of St. Georg was contained within the fortress, but in 1005 it was moved to Stein am Rhein (now in Switzerland), and the Swabian dukes lost control of Hohentwiel. In the later Middle Ages the noble families von Singen-Twiel (12th–13th centuries), von Klingen (to 1300) and von Klingenberg (to 1521) resided here. In 1521, it was passed on to Duke Ulrich von Württemberg, who developed Hohentwiel into one of the strongest fortresses of his duchy. During this time, it began to be used as a prison and in 1526, Hans Müller von Bulgenbach, a peasant commander, was imprisoned there prior to his execution.[1]

The fortress resisted five Imperial sieges in the Thirty Years' War, under the command of Konrad Widerholt[2][better source needed] between 1634 and 1648.[3] The effect was that Württemberg remained Protestant, while most of the surrounding areas returned to catholicism in the Counterreformation .[4] The castle served as a Württemberg prison in the 18th century and was destroyed in 1800 after being peacefully handed over by the French. Today the former fortress Hohentwiel is the biggest castle ruin of Germany.