The citadel in Copenhagen, normally referred to as Kastellet, is a well-preserved, star-shaped fortress that was built in the 17th century to guard the approach to the harbour. 

It was well over a kilometre east of the east gate of the city with a clear view over the sound. Work started in 1626, in the reign of Christian IV, with the construction of St Anne’s Redoubt - Sankt Annæ Skanse - but work and ongoing alterations continued through to the 1660s, with major remodelling and improvements after the Swedish Army attacked the city in the war of 1658-60. The complex of defensive embankments, moats and military buildings were ostensibly complete by the 1720s in the arrangement that can still be seen today. 

The main central area has five bastions (1-5) where the embankments are about 20 metres high rising sharply from an inner moat. Outside the bastions there are outworks with four ravelins (6-9) and three counter guards (10-11) that on the land side of the citadel form a narrow bank between the inner and an outer moat. This is known as Smedelinien (the Blacksmiths Line) as the works included two forges. The embankments (13) here are much lower so they do not break the line of fire from the top of the main bank but are high enough to protect an inner pathway, on the side towards the inner moat, so that soldiers could be moved quickly to a point under attack but would have some protection from the fire coming from an attacking force outside the fortress.

Outer redoubts (14-16) beyond the outer moat on the north side were constructed to provide a first line of defence for any attack from the land.

There are two gateways into the inner area … both with an outer redoubt guarding the approach to a first bridge that cross over to a ravelin - a triangular island with outward angled faces to allow for protecting fire from there across the outer moat. From the inward facing base of the island a bridge crosses to the gatehouse proper. The two bridges were not in line so anyone attacking and crossing the first bridge could not fire directly towards the gate.

Both gateways have long narrow tunnels through the embankment again to contain and control any attack.

The south gate from the city is called the King’s Gate (17) and the far or north gate is the Norway Gate (18). Both were constructed in their present form in 1663. Immediately inside both gateways were guard houses and pathways set at an angle to give access to the top of the embankments.

It is the scale of earthworks that is so impressive. The citadel is 550 metres from the approach to the King’s bridge to the far side of the moat beyond the Norway Gate and the walk around the outside of the moats is 2.5 kilometres.

Clearly work on such a large scale meant complex setting out, levelling of the ground, the construction of major earthworks and water works which would have required the expertise of an engineer. Records show that from about 1616 a Dutch engineer, Johan Semp was employed by Christian IV to draw up a plan for Christianshavn and its defences so some foreign expertise was available although it is also thought that Semp returned to the Netherlands in 1620 so could not have supervised directly the work at the new citadel. Almost certainly, the Danish army would have included military engineers - who were required for setting out trenches in a battle, planning attacks on fortified sites or improving defences - so presumably some Danish military engineers would have been involved in setting out and supervising the construction of the earthworks of the Kastellet.

Henrik Rüse, another Dutch engineer, was certainly employed after 1660 and was responsible for the design of the barracks and store houses.

An early map, dating from the middle of the 17th century, shows a harbour within the defences. It was oval in shape and was entered through a narrow channel from the sea with a breach in the embankment at the centre on the east side. It was immediately behind the commander’s house that was built in the early 18th century after the internal dock had been filled in.

A map of the city in 1685 is important for several reasons. It shows the Kastellet in it’s final form. There are still areas of water within the defences with two long rectangular areas running north south immediately inside the east embankment but curiously no way through from the sea. In the centre between the areas of water is just a narrow causeway running out to where there is now a tunnel through the embankment. Were these areas of water for a fresh-water supply for the fortress or even possibly for fish tanks for a supply of food through a potential siege?

A new city gate and east bridge at Østerport (19), just below the citadel, had the same arrangement as the gates to the fortress with the first bridge crossing to a Ravelin and from there, set on a different alignment, a second bridge across to the gateway itself for access to the city. Again there were guard houses on the ravelin.

What is also important to note is that the Kastellet was not, at that stage, quite as land locked as it appears to be now. The line of the promenade along the shore and the building of the Free Port to the north, just over a hundred years ago, has encroached on the defences. In the late 17th century there was only a narrow outer defence between the sea and the east embankment … presumably to stop attacking war ships from being able to sail right up against the east embankment to bring canon and men in to attack from a higher level … and the north-east side of the fortress looked out northwards over open sea to defend the approach to the harbour. The map also shows Christianshavn and its earliest extent so that is before the extensive yards and docks of the naval base were built across the north shore of Amager between the new town and the sound.

A map of 1835, only twenty or so years before the defences around the city itself were dismantled, shows the final development of the defences around Kastellet with the naval base with it’s own embankments and bastions to protect it on the Amager side and a gun emplacement facing out to the sound The actual harbour entrance had been narrowed and was therefore more easily protected; fortresses out at sea prevented attacking vessels getting too close without being, at least able to return some defending fire and a redoubt further north up the coast covered the shore across the ends of the outer lakes so an army would find it more difficult to land between the inner and outer defences of the city.


There are a number of important buildings within the Citadel.

The rows, the Stokkene or barracks, are six long blocks that were constructed in the early 18th century as part of the work by Henrik Rüse. (22-27) These housed the garrison in dormitories that were four metres by four metres each with two triple bunks, a table and two benches.

Initially the commander occupied the rooms at the south end of General Stock but then was given his own rather grander accommodation facing the church.

The garrison here had 1,800 men. Curiously, there is no obvious evidence for a kitchen, bakehouse or brewhouse that would be necessary although the north east barrack has a large chimney stack just in from its south end which might indicate a service room and on the west side of the north Magasin is a an addition with large windows suggesting a high space rising through two floors so possibly another service room … cooking and baking and brewing all generated a lot of smoke and heat so higher ceiling heights helped to create a better space in which to work. 

In 1704 the church (28) on the west side of the central parade ground was built and in 1725, curiously, a prison (29) was added across the back of the church with small internal windows in some of the cells that look down into the church so prisoners could follow the service. There are records for some prisoners being held here for long sentences of many years if not decades.

The new house for the Commander (30) was built opposite the church in 1725 - the architect was Elias Häuser.

With the threat that the garrison here might have to withstand a long siege, there were substantial store houses constructed, in form like contemporary warehouses in the main harbour, with a granary to the north of the church, Nordre Magasin, (31) and an arsenal (32) south of the church, Sodre Magasin.

There were gunpowder stores built in 1712 at the Queen’s Bastion and the Count’s Bastion (2 and 3) which both had massive thick walls and were tightly encircled by high embankments in the hope that if there was a fire and an explosion then the force of the blast would go up rather than out … in the 16th and 17th centuries gunpowder was unstable and there was always the threat of a major and devastating accident.

Funen’s Ravelin had one of the two forges (8) within the defences and there was a forge on Falster’s Counter Guard (12) in 1709 and that was rebuilt in 1888. Presumably the forges were used for repairing weapons. I cannot see any evidence within the present buildings for stables … presumably the garrison did not include cavalry although the Commander at least must have had a carriage and working horses would have been used for moving armaments and stores.

In a siege, fresh food would have been in short supply but the crucial requirement were water and flour. The windmill on the King’s Bastion (1) dates from 1847 replacing a windmill of 1718. Grain would have been stored in the warehouses and it would have been ground as and when flour was needed.


The church was restored in 1985 and the embankments were restored and some sections of the moats, that had been filled in, were reinstated in 1998-9.

A railway had actually been built through the east side of the citadel running from the main harbour dock, from close to the Customs House, crossing just above the level of the moat to the south-east bastion which had been breached for the railway and then ran due north behind the commander’s house before cutting through the embankment just east of the north gate before entering the area of the quays and dock buildings of the Free Port. The railway closed in 1985 and the engineers Jeppe Aagaard Andersen restored the earthworks so there is now little to indicate that the railway was ever there although the ornate ironwork bridge from the Gefion fountain across to the Langelinie promenade was built simply to get people over the rail tracks and at the other side of the citadel the road used by tourist coaches to take people to see the Little Mermaid actually crosses over a second rail bridge although the train tracks became redundant thirty years ago.


Map showing the Free Port and the railway from the main harbour that cut across the east side of the Kastellet. Note, when this map was produced, Østerport was a terminal for the railway from the north. It was only in 1917 that a series of cuts and tunnels were constructed so that trains could continue through to the central station.



The view from the quay of the harbour looking along the route of the railway where it went under the iron footbridge, went over the moat and through the embankment of the south-east bastion


View from the embankment looking north along the route of the railway that went over the moat here and under the road bridge before continuing on to the Free Port beyond