Bischofszell castle was built in the 12th/13th century. It was damaged by the city fire in 1419 and repaired soon thereafter. During the 17th and 18th century the castle was expanded and totally renovated. The newly founded Canton of Thurgau took over the castle in 1798, but sold it in 1811 again. About 1838 the west part collapsed, and in 1843 the keep was broken up. Since 1930, the castle has been owned by the municipality.
The old bridge, constructed in late gothic style, was inaugurated in 1487. It is the oldest bridge in the entire region.
Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.