King Christian IV of Denmark initiated Kastellet's construction in 1626 with the building of an advanced post, St. Anne's Redoubt (Danish: Sankt Annæ Skanse), on the coast north of the city.

The redoubt guarded the entrance to the port, together with a blockhouse that was constructed north of Christianshavn, which had just been founded on the other side of the strait between Zealand and Amager.

At that time the fortifications only reached as far north as present day Nørreport station, and then returned south east to meet the coast at Bremerholm, the Royal Shipyard.

After the Swedish siege of Copenhagen (1658–1660) the Dutch engineer Henrik Rüse was called in to help rebuild and extend the construction.

The Blacksmith's Line (Danish: Smedelinien) is a system of outworks, separating the inner and the outer moat, located to the south and southwest towards the city.

It was built in 1725 in the Baroque style by architect and master builder Elias Häuser who also designed the first Christiansborg Palace which burned in 1794.

Built in yellow-dressed masonry with white detailing, it consists of two floors under a red tile roof.

[3] The Rows (Danish: Stokkene) are six two-storey terraces which were originally built by Henrik Ruise as barracks for the soldiers based at the Citadel.

They were to store everything need in the event of a siege, and could when full feed the 1,800 men of the garrison, other personnel, and their families for four years.

It was designed with massive walls and a slightly vaulted ceiling to ensure that a possible explosion would move upward and thereby cause a minimum of damages to the surroundings.

The Kastelskirken ("Citadel Church") was built in 1703–4 in heavy Baroque style during the reign of King Frederik IV.

The English explorer and pirate John Norcross was the person to be imprisoned at Kastellet for the most extensive period.

The mill at Kastellet is the last which is still working, while another one, Lille Mølle at the Christianshavn Rampart, was transformed into a private home in 1915 and now survives as a historic house museum.

Russian Empress Consort Maria Feodorovna, daughter of Christian IX of Denmark, got her rye flour from the mill at Kastellet.

The Army's Bread Factory would send it to the Imperial Court in Saint Petersburg where she was served øllebrød every morning in the Anichkov Palace.

Military activity in the area includes use by the Home Guard, Defence Intelligence Service, the Judge Advocate Corps, and the Royal Garrison Library.