Fortifications of Copenhagen ( 17th century ) The fortifications of Copenhagen underwent a comprehensive modernization and expansion in the 17th century . 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 . The new fortifications relied on the existing , medieval fortifications of the city but the fortified area was extended and a defensive ring around the city completed particularly with new edifices facing the sea . The ring fortification consisted of four bastion ed rampart s and an annexed citadel as well as various outwork s . Though largely developed to a final form in the 17th century , the fortifications remained in use until the second half of the 19th century , when they finally , a long time overdue , were decommissioned . 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 . The grounds were to a large extent laid out as parks , forming a green band around the city centre still known as the Fortification Ring , as well as for construction of a number of public buildings , including the new Copenhagen City Hall as well as a number of museums . History . Christian IV ' s modernization project . Christian IV ' s modernization of the fortifications of Copenhagen commenced in 1606 and would take 20 years to complete . The course of the medieval fortifications was kept but Slotsholmen was now incorporated into the complex . A large bastion in masonry was constructed on its southwestern tip and connected to Vestervold by a vaulted dam known as Løngangen . In the same time , Østervold was taken around parts of Bremerholm to meet the sea . A total of 12 bastions were constructed and just outside the entire fortification a moat was dug . Due to topographical variations in the terrain , it was constructed as a series of basins , separated by dams , to solve the problem of variations in the terrain . The uppermost basin was fed by water from Peblingesøen . The Western and Northern City Gates were also renovated and given tall spire s and a new Eastern City Gate was built . From 1618 - 23 Christianshavn was laid out and incorporated as a privileged market town . Strategically situated in the middle of a shallow - watered , marshy area north of Amager , the town was fortified with low earthworks facing Amager . The rampart was constructed with four and a half bastions and a gate , known as Amager Gate . To guard the northern entrance to the port , a blockhouse was constructed on the shallow - watered Refshaleø in 1624 . 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 . This work was begun in 1627 . Expansion of the fortified city . As part of his aspirations to strengthen Copenhagen as a regional centre , Christian IV decided to expand the area of the fortified city northwards . As early as 1606 , when his modernization of the fortifications began , he had purchased 200 hectares of land outside the Eastern City Gate . 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 ) . 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 enermy forces in the first half of the 1640s and the Kingdom ' s very existence had been threatened , work on the fortifications was resumed . The new Østervold was constructed and a new project for the fortress at Sankt Annæ Skanse , with the layout of a bastioned pentagram , was completed in 1661 . Decommissioning of the fortifications . The British bombing of Copenhagen during the Battle of Copenhagen in 1807 made it clear that the city ' s fortifications were outdated but during the years of economic constraints that followed , no action was taken . 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 . In 1852 , the Line of Demarcation was partially disabandoned but work to maintain and improve the ramparts were carried out as late as 1856 - 57 . In 1868 a law finally provided for the official abolishment of the demarcation statutes and the disabandonment of the fortifications proper . In 1856 - 58 the city gates were dismantled . These provisions did not apply to fortifications at Christianshavn and Kastellet . Christianshavn ' s ramparts were extended as late as 1868 - 1870 with a rampart along the east coast of the newly reclaimed Refshaleø , which only a few years later was rented out to the shipyard Burmeister & Wain . The fortifications at Christianshavn remained in use into the 20th century . Some areas were opened up in the late 1910s , and the last areas were not made public until 1961 . Fortifications . Ramparts . The ramparts generally consisted of large earthworks with a ditch in front of it . As part of the improvements , numerous bastions were constructed along their course . In 1781 , after extensive work on the fortifications in the preceding years , the bastions were given official names according to group : The bastions in Copenhagen were named for officers of note from the siege or other events of the early absolute era , the bastions at Christianshavn were named for powerful animals and at Kastellet . Since 1669 , the bastions at Kastellet had been named for members of the Royal family and the King ' s lands . Nørrevold . Nørrevold ran from Jarmers Tower to a site just east of Nørreport , at the junction of today ' s Gothersgade and Øster Voldgade . Vestervold . 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 . The extension included three new bastions , two of which were located on reclaimed land . Østervold . Originally Østervold ran from a location just east of Nørreport along today ' s Gothersgade to Østerport ' s original location at the end of Østergade . 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 . Christianshavns Vold . The first Christianshavns Vold , constructed around 1620 , had 4 and a half bastions . In the 1670s , when Vestervold was extended to reach the sea , Christiansvold was moved and extended to match the new course of Vestervold . The new Christianshavns Vold had 5 very large bastions . Around the entire complex was a moat with a protecting counterscarp . From 1682 - 92 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 . The extension included 7 new bastions , named for current members of the Royal family . The last extension of Christianshavns Vold was constructed as late as 1878 - 82 , when a rampart was constructed along the eastern margin of the newly reclaimed Refshaleø . City gates . The gates that once guarded the entrances to the City of Copenhagen through the City Ramparts were stone buildings that had a single archway through the middle for traffic , protected by gates and portcullises . There were four gates affording access to the city . Østerport . Østerport was originally located at the end of Østergade , where Kongens Nytorv lies today . When the fortified city was expanded in the late 17th century to make room for the new Royal square and the district Saint Anne ' s Town , Østerport was dismantled and a new gate built at a site close to present day Østerport station . While the original East Gate faced east , the new gate was very close the northernmost point of the city . It is uncertain when the new Østerport was built but it may have been as early as 1647 . It was also referred to as the Elsinore Gate . Its original design is unknown but in 1708 it was rebuilt by Frederick VIII to a fairly modest design . The gate was dismantled in 1857 . Nørreport . Nørreport was located at a site where Nørreport station lies today . Nørregade , which led to the original gate , is named for it . Due to its location , it was the gate used by travellers from Norway and Sweden , arriving via Elsinore , as well as Northern Zealand . 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 . In 1671 , during the reign of Christian V , an older gate was replaced by a new one , built to the design of Lambert van Haven . It was the tallest and finest of the city ' s gates with ornamentation in sandstone . It was dismantled in 1857 . Vesterport . The first Vesterport was erected in 1588 and later rebuilt in stone by Frederik III in 1668 . The new gate was almost 4 metres wide and 4½ metres tall and as an architectural curiosity , with canon barrel s used as columns to support the main cornice . The gate was renovated in 1722 by Fredecrik IV . Vesterport was the most fortified of the city ' s gates . It was the gate most used for transportation of goods from Zealand . Opening to the main road which led to Korsør , it was also through this gate that travellers from Jutland and Funen would normally arrive . Amagerport . Amagerport was rebuilt in 1724 and dismantled in 1857 . Citadel . As part of Cristian IV ' s endeavour to improve the fortification , he planned and commenced the construction of a citadel known as Kastellet , constructed in connection with the ramparts in the form of a pentagram . Construction began in 1626 with the building of an entrenchment in the northern part of the defense wall of the city . The original plans included construction of a castle at the site for the King to seek haven in the event of siege , but this part of the plan was dropped on account of economic constraints . Construction continued with his successor King Christian III . After the Swedish siege on Copenhagen ( 1658 – 1660 ) the Dutch engineer Henrik Rüse was called in to help rebuild and extend the construction . The fortification was named " Citadellet Frederikshavn " ( " The Frederikshavn Citadel " ) , but it is better known as Kastellet ( " the citadel " ) . Outside the ramparts . Demarcation line . Immediately outside the ramparts , there was a no - build zone , known as the Line of Demarcation ( Danish : Demarkeringslinjen ) . The demarcation line was introduced in 1661 after the Assault on Copenhagen . The Lakes . 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 watermill s , 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 . The levee at Peblinge Sø was expanded and another dam was constructed , which resulted in the creation of Sortedams Sø . In the beginning of the 17th century , Sankt Jørgens Sø was created , as a result of further damming . As a results of these efforts , it was now possible to flood the banks and lakes in case of an attack on the city . Other uses . Gunpowder magazines . Many gunpowder magazine s were located in the fortifications After his appointment as Naval Building Master at Holmen , Hans van Steenwinckel the Youngest was responsible for the construction of two gunpowder magazine s at the Christianshavn Rampart . Construction of the first magazine , located at Vilhelms Bastion , was commenced in 1688 , while the second one , built to a similar design at Carls Bastion , began two years later . The gunpowder magazine at the Eastern Rampart exploded on two occasions . The first time was on 16 December 1658 , during the Swedish siege of Copenhagen in the Second Northern War . On 31 March 1779 it exploded again . Seven people were killed and 47 were injured . It was subsequently rebuilt and not decommissioned until 1872 . Windmills . Many of the bastions were used for the construction of wind mills . Due to their height they offered particularly good wind conditions . In the same time , a fortified city needed secure supplies , including supplies of flour and rolled groats , in the event of siege . In 1800 , a total of 16 windmills were found on the ramparts of Copenhagen . In 1669 – 70 windmills were constructed on both of the bastions flanking Amager City Gate in Christianshavns Rampart , then known as the " Mill Bastion " ( now the Elephant ' s Bastion ) and the " Bastion at the Church " ( now the Lion ' s Bastion ) . " Breslaus Mølle " on the Mill Bastion was demolished in 1842 . " Little Mill " on the Lion ' s Bastion was originally a post mill but it was destroyed in a storm and replaced by a smock mill in 1783 . It remained in use til the late 19th century , from 1832 supplemented by a steam mill which remained in use until 1909 . 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 . It was known as " Luciemølle " or " Lusse Møllen " . 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 Wastern City Gate . in 1692 a windmill was also built at Gothersgade , on the old Eastern Rampart . " Dronningens Mølle " ( English : Queen ' s Mill ) was located on Rosenkrantz ' Bastion in the Eastern Rampart . It was completely destroyed when the gunpowder magazine at the Eastern Rampart exploded on 31 March 1779 . It was rebuilt but torn down in 1895 . When the British besieged Copenhagen in 1807 , it was feared that they would destroy the mills on the fortifications . Therefore two extra mills were constructed on less exposed locations , one at Sølvgade and one on Nyholm . The fortifications today . Fortification Ring . The grounds which used to be occupied by the fortifications are still known as the Fortification Ring ( Danish : Fæstningsringen ) . From the ramparts were first decommissioned and purchased by the City of Copenhagen , their grounds have been dominated by parks and other recreational uses . It is still municipal policy that the Fortication Ring is maintained and developed as a green band within the urban area of the city . Parks located within the Fortification Ring include Østre Anlæg , University of Copenhagen Botanical Garden and Ørstedsparken . The preserved parts of the fortifications at Christianshavn and Kastellet are also green and serve as parks . This also applies for Freetown Christiania which is partially located on the northern part of the Christianshavn Ramparts . The area also houses a number of museums , including the National Gallery , The Hirschsprung Collection and Lille Mølle .