The island is dominated by the vast Christiansborg Palace which houses the Danish Parliament, the Supreme Court of Denmark, the Prime Minister's Office and the State Rooms of the King.

On the largest of these, Strandholmen (English: Beach Islet), Bishop Absalon of Roskilde constructed a small castle in 1167.

Probably during the reign of Christian III a building was constructed on the quay of the canal in front of the castle to house the Chancellery.

[citation needed] Under King Christian IV Slotsholmen saw considerable development, especially in the southern part of the island.

By the time of the introduction of the absolute monarchy in 1660, the role of Slotsholmen as the centre of administration was firmly established.

[citation needed] During the reign of King Frederick III, further lack of space in the castle led to the construction in 1665-1673 of an additional building between the Supply Depot and the Arsenal.

[citation needed] During the reign of King Frederick IV, a magnificent administration building was constructed in 1716-21 next to the palace adjacent to the Supply Depot.

The new chancellery building was connected to the castle by an arched passageway, thus allowing the king to stay in close contact with his government.

[citation needed] However, just two years after the rebuilding was completed, the Copenhagen Castle was demolished in 1731 to give room for three consecutive Christiansborg Palaces, the two first of which were destroyed by fires (in 1794 and 1884).

It was at this very spot, where the city ramparts at that time was located, that the Swedish troops made their principal attack.

The nature of the course makes it unusually good for spectators and that combined with the historical surroundings have gained it a reputation as one of the best open water swim competitions in Europe.