Kalø Castle was founded in 1313 by the Danish king Erik Menved in order to establish a stronghold in northern Jutland to counter the ongoing rebellions by the local nobility and peasants against the crown. The castle was successful and from the 15th century and onwards the castle had a more peaceful role as the local administrative center. King Christian II held the future Swedish king Gustav Vasa captive at Kalø during 1518-1519, until he escaped.
When king Frederick III converted the elective monarchy into an absolute monarchy by the revolution of 1660 in Denmark, the castle lost its function. In 1661, Frederick III gave Kalø to Ulrik Frederik Gyldenløve, who in the following year (1662), tore down the now abandoned castle. The material was used to build his private palace in Copenhagen, now called the Charlottenborg Palace. Today the castle ruin is owned by the Danish State.
References: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.