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:The Château du Lude is one of the many great châteaux of the Loire Valley in France. Le Lude is the most northerly château of the Loire Valley and one of the last important historic castles in France, still inhabited by the same family for the last 260 years. The château is testimony to four centuries of French architecture, as a stronghold transformed into an elegant house during the Renaissance and the 18th century. The monument is located in the valley of Le Loir. Its gardens have evolved throughout the centuries.