Looking at maps of the city, one of the most striking features is the long line of narrow lakes that run in a gentle arc around the west side of the inner city and form a distinct break between the inner historic centre and the later areas of Østerbro, Nørrebro and Frederiksberg.
There are three lakes - from the north end first Sortedams Sø, the longest lake divided into two parts by a road, then Peblinge Sø, the two lakes separated by the Dronning Louises Bro, and, at the south end, Sankt Jørgens Sø, again divided into two parts by a road. From the top end at Østerbrogade to Gammel Kongevej, below the level of the south lake, is just over three kilometres and the lakes, although they vary in width, are around 200 metres wide, from the inner edge to the outer shore, so this is a very large area of water.
The lakes, initially spreading over a larger area and flanked by marshy ground, provided an outer defence to the city that was a physical barrier that any attacking army would have to cross and the water here also maintained the level in the outer moat of the defences. The lakes provided the city with a store of fresh water and water for irrigation.
The earliest settlement appears to have been on a gentle slope running down to the shore and looking across to the large low island of Amager. With the density of building in the city now, it is difficult to appreciate the natural topography but clearly the lakes are in a slight hollow beyond the slope and the early town and are barely above sea level. Østerbrogade is at the highest point and then each lake is at a lower level until you reach Gammel Kongevej where the road itself is actually around a metre below the level of the surface of Sankt Jørgens Sø.
Looking at the map there appears to be four bridges crossing the lakes although only the road at Dronning Louises Bro between Sortedams Sø and Peblinge Sø with its three central arches is actually a bridge with the water level the same on both sides. The other roads, Solvgade running across to Fredensgade, Gyldenløvesgade and Kampmannsgade are on dams. In fact Kampmannsgade has embankments on either side and the sloping road is actually well below the water level of the lakes on either side.
The upper lakes have low stone retaining walls and gravel pathways forming an edge to the water but at Sankt Jørgens Sø there are natural grass banks with willows and reed beds but again these are man-made embankments and particularly on the outer shore the gardens and houses and apartments along Vodroffsvej are well below lake level.
Historic maps show how the lakes have changed over the last four centuries and in the late 17th century and through into the 18th century the lower lakes had a much more irregular outline and covered a much wider area indicating the natural contours of the underlying topography. In fact the map of 1674 shows a lake north of Østerbrogade and a simple dyke between that lake and the sea and, at the south end, lakes or marsh continuing round to Køge bay so at that time the city was surrounded by water.
By 1705 the moats and embankments of the defences encircled the city and there were regulations to restrict buildings beyond although there were outer defences beyond the lakes. By the late 18th century there were roads beyond the lakes with some houses with gardens running down to the far shore of the lakes. By 1860, shortly before most of the moats and defensive embankments were removed, the lakes were close to their present extent and shape.
Now the lakes are an important resource. They provide a strong sense of clearly-protected open space, with wild life - Fugleøen, the island on the outer edge of the northern lake, has a breeding colony of cormorants and there are nesting swans on the lower lake. Thousands of people live in the apartments and houses overlooking the lakes and the lakes are a major resource used for leisure and for people walking and running.
Crossing over Dronning Louises Bro and heading into the city for the evening