In Brønshøj in Copenhagen you can find these strange copper structures. Resembling old style army tents they are a monument to Carlstad, a Swedish encampment that lay here during the siege of Copenhagen in 1658-60. With 30.000 "citizens" this was almost a town in its own right. The Swedish forces never managed to conquer Copenhagen, even though they tried a massive assault February 11, 1659. The assault failed with thousands of Swedish dead and only about 30 Danish casualties. When the Swedish King Charles X died the following year the war ended.