Uster Castle was built probably around 1200 by the House of Rapperswil. After the Appenzell wars Hans von Bonstetten concluded a pact with Zürich, and became a citizen of the city of Zürich respectively claimed the so-called Burgrecht in 1407. From that moment, the castle in time of war could be strengthened by a Zürich garrison. As an Austrian vassal, Zürich guaranteed a neutral status to the Bonstetten family, particularly during the Old Zürich War when the neighbouring town of Greifensee was besieged and destroyed by Old Swiss Confederacy marauders; the bodies of the defenders were buried at the Uster church.
In 1492 a fire destroyed the castle. The owners changed the following centuries many times. In 1852 the castle became the seat of the district administration, and the tower was used as a prison. In the same year the castle was rebuilt, again, and a restaurant opened. Since 1995 the castle houses the private boarding school, and the former restaurant Burg was rebuilt in a steakhouse in 2009.
From the first construction phase, the lower section of the tower, up to the level of the upper floor of the today's boarding school's building around the tower base, is preserved, but never was scientifically examined, as well as the surrounding area of the plateau. The core of the present tower measures about 11 metres.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.