The project was commenced and was largely the masterplan of Christian IV in the early 17th century but was continued and completed by his successors.

Today only the Christianshavn Rampart and the citadel Kastellet remain intact, while the rest of the fortifications were dismantled in the years after its demise.

On the Zealand side of the harbour, north of the city, an advanced post, named Sankt Annæ Skanse (English: St. Anne's Redoubt) was constructed, on the site later to become Kastellet.

As part of his aspirations to strengthen Copenhagen as a regional centre, Christian IV decided to expand the area of the fortified city northwards.

His intention was to redevelop this area into a new district referred to as Ny København (English: New Copenhagen) or Sankt Annæ By (Saint Ann's Town).

[2] The plan was to change the course of Østervold, which at that time made a bend and ran along what is today Gothersgade and Kongens Nytorv.

The new Østervold would be a direct extension of Nørrevold, connecting it to Sankt Annæ Skanse, thereby increasing the area of the fortified city with approximately 40%.

However, the 1630s was a time of economic crisis and both Sankt Annæ Skanse and the new course of Østervold was delayed with no major work going on during that decade.

After both Jutland and Scania had been occupied by enemy forces in the first half of the 1640s and the Kingdom's very existence had been threatened, work on the fortifications was resumed.

In 1840 Christian VIII appointed a national defense commission which two years later recommended that the existing fortifications be decommissioned.

At the outbreak of the First Schleswig War in 1848, nothing had happened and considerable work was carried out to strengthen the ramparts around the city gates in the event of a German attack.

Nørrevold ran from Jarmers Tower to a site just east of Nørreport, at the junction of today's Gothersgade and Øster Voldgade.

In connection with a modernisation of Vestervold in the 1660s, the ramparts were extended towards the south from Vesterport all the way to the coastline and into the water on reclaimed seabed.

As result of Christian IV's efforts to modernize the fortifications, the southern end of Østervold was continued around parts of Bremerholm.

After the expansion of the fortified city in the 1650s, Østervold continued Nørrevold in a straight north-eastern direction, connecting the fortifications to the north side of Kastellet.

From 1682 to 1692 Christianshavns Vold was extended once more, this time northwards, to guard the entrance to the harbour and protect the new base for the Royal Fleet at Nyholm.

Since the royals often resided at Frederiksborg Palace during the summer, arriving and departing through Nørreport, the street immediately inside the new gate was named Frederiksborggade.

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

[1] The row of lakes today known as Søerne used to be located just outside the fortifications, running along Nørrevold as well as parts of Østervold and Vestervold.

They originate in a need for dammed water for watermills, leading to the creation of the first lake, but after a siege of Copenhagen in 1523, it was decided to extend the entrenchments for strategic purposes, incorporating them into the defence of the city as an extra barrier.

[7] Also in 1669, the miller Hans Hansen obtained permission to build a mill on Gyldenløves Bastion, just south of the Western City Gate.

Whether it later burned or was never built is uunknown, but in 1697 Jürgen Gosbruch, another miller, received permission to build a windmill on the same site.

Some time during the 1790s, another windmill, known as Store Kongens Mølle (English: Large King's Mill), was built on Shacks Bastion on the other side of the Western City Gate.

It is still municipal policy that the Fortification Ring is maintained and developed as a green band within the urban area of the city.

[10] Parks located within the Fortification Ring include Østre Anlæg, University of Copenhagen Botanical Garden and Ørstedsparken.