History

Sønderborg Castle was probably founded by Valdemar the Great in 1158 as a fortified tower to provide protection against attacks by the Wends. It expanded gradually. Around 1350, the castle expanded significantly with the addition of the Blue Tower and huge outer walls. In 1490, the fortress became the property of the Crown. Both King Hans and his son Christian II extended Sønderborg Castle and made it into one of the country's strongest fortresses.

In 1532, Christian II was lured into an ambush and held captive in the fortress for 17 years. Legend would have it that he was confined to the Blue Tower, but in reality he was probably allowed freedom of movement within the outer walls.

Christian III had architect Hercules von Oberberg modernise the fortress from 1549-57. King Hans' west wing was preserved and a further three wings added in the new Renaissance style. After Christian III's death in 1559, Hercules von Oberberg built the unique castle chapel in 1568-70 for Queen Mother Dorothea. After Dorothea's death the castle passed into the ownership of the Dukes of Southern Jutland until 1667, when it became a Danish estate and was more or less unused until 1718.

In 1718-26, Frederik IV had the castle rebuilt in baroque style by the contractor general Wilhelm von Platen. New roofs and windows were installed in straight, even rows. In 1755, Blue Tower was demolished and in 1764 the castle passed into the hands of the local dukes again and was rented out as a warehouse. After 1864, the castle became Prussian property and served as barracks until reunification in 1920.

The last Duke, Ernst Günther, allowed Sønderborg County Museum to move into a part of the castle in 1920. The Danish state took over the castle in 1921 and allowed several institutions to use it as long as they paid heed to the expanding museum.

They Royal Inspector of Listed State Buildings Peter Koch and Jørgen Stærmose conducted a thorough restoration of the castle from 1964-73. The castle was more or less restored to its 1720 appearance - the windows from the barracks era were even replaced with "masks" - windows with broad wooden frames made of planks like the ones in Platen's castle.

Sønderborg Castle is owned by the Danish state, run by the Palaces and Properties Agency and used by Sønderborg Castle Museum, which is jointly owned by Sønderborg Municipality and South Jutland County.