Adolf Fredriks kyrka ("The Church of Adolf Frederick") was built in 1768-1774, replacing a wooden chapel from 1674, which was dedicated to Saint Olof. René Descartes was first buried to the cemetery in 1650 (before his remains were moved to France). Inside the church is a memorial to the memory of Descartes installed by Gustav III. Other famous people buried in the church cemetery include Swedish Prime Minister Olof Palme who was assassinated only a block from the church, as well as Prime Minister Hjalmar Branting.
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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.