At this point the loop is only 40 meters wide. On the opposite Reesholm peninsula there used to be a wooden structure in the loop. It was part of the defense system of the Danewerk. The lake barrage extended parallel to the fairway for about one kilometer to the east. It controlled the transition at this narrow part of the fairway. The lake barrier closed the gap between the ramparts of the Danewerk west of the Schlei and the Osterwall at the transition to the Schwansen peninsula.
Today the structure made of oak planks is no longer visible at the point. However, some components up to 1.40 meters high have been preserved under water.
And what is the Danewerk? Well, over 1,000 years ago, in the Viking Age, Danes, Frisians, Saxons and Slavs met here in the border region between Scandinavia and Central Europe. Danish kings began to expand the Danewerk as a border fortification. In this way they secured the southern border of their empire and the trade route between the North and Baltic Seas. The Danewerk consisted of earthworks, walls, ditches and a barrage in the Schlei. The most important trading center and transport hub was Haithabu. (Source: information board)