The construction of the Klingnau castle, originally the seat of the Klingen family, was started in 1240. Until 1269 a manor house stood on the grounds. After 1331 the outer walls were added. In the second half of the 14th century the Bishop of Constance was often a resident in the castle. He ordered further improvements and expansions.
In the late 16th century, the castle, which was the seat of the bailiff from Constance, in such bad condition that the Swiss Confederation demanded a renovation from the bishop. In 1804 the castle went to the newly formed Canton of Aargau, who auctioned it off in 1817. As a result it has been used by various industries, until the 20th century when it was taken over by a foundation.References:
Sirmione castle was built near the end of the 12th century as part of a defensive network surrounding Verona. The castle was maintained and extended first as part of the Veronese protection against their rivals in Milan and later under the control of the Venetian inland empire. The massive fortress is totally surrounded by water and has an inner porch which houses a Roman and Medieval lapidary. From the drawbridge, a staircase leads to the walkways above the walls, providing a marvellous view of the harbour that once sheltered the Scaliger fleet. The doors were fitted with a variety of locking systems, including a drawbridge for horses, carriages and pedestrians, a metal grate and, more recently, double hinged doors. Venice conquered Sirmione in 1405, immediately adopting provisions to render the fortress even more secure, fortifying its outer walls and widening the harbour.
Thanks to its strategical geographical location as a border outpost, Sirmione became a crucial defence and control garrison for the ruling nobles, retaining this function until the 16th century, when its role was taken up by Peschiera del Garda.