Carlstad was a short lived fortified town in Denmark built by the forces of King Charles X Gustav of Sweden during his siege of the Danish capital, Copenhagen, 1658 - 1660. Carlstad's size rivalled the besieged Danish capital, reaching a peak of approx. 30,000 inhabitants. The modern Copenhagen district of Brønshøj, Bellahøj and Utterslev are located on or near the site. Several nearby streets are named for it; e.g. Svenskelejren (The Swedish Camp) and Skansebjerg (Trench Hill). The only preserved building extant at the time of the encampment is Brønshøj Church, used as a weapons store during the siege.
After a successful campaign of Jutland, Funen, and Zealand, Charles X Gustav began a siege of Copenhagen intending to remove his country's traditional enemy once and for all. He decided to encamp his army to the west of the city with its centre on the village Brønshøj, now a northwestern Copenhagen district. This site occupied an elevated position 4 km from the Danish capital.
At its peak, Carlstad's population, primarily consisting of army personnel and followers, rivalled that of Copenhagen itself. The topographical features of the site were applied for strategic use. With its location significantly higher than Copenhagen, Bellahøj ridge provided a natural eastern rampart, also providing a view over the besieged city. Carlstad's northern site was flanked by a great marsh. The land descended to the west and south of the camp.
No evidence of the fortress earthwork have been preserved. A number of artefacts and models of the fortress are displayed at Brønshøj Museum.