Sirksfelde Ringfort

Big and impressive, she rises before us as we approach her - the Sirksfelde Ringwall. An almost perfect circle of almost one hundred meters in diameter makes it one of the largest in the area. The good preservation presumably results from the fact that, according to excavations, it was only used for a short time and thus was saved from destruction. Well, it can be done on the whole round.
slawenburgen.hpage.com/schleswig-holstein.html#Sirksfelde

The Slavic rampart of Sirksfelde, a municipality in the Duchy of Lauenburg in Schleswig-Holstein, is a good one kilometer south of the town on the L 200 in the forest.The approximately 100 meter high castle wall dates from the 8th and 9th centuries and was located in the territory of the Obodrites. As archaeological studies have shown, the Niederungsburg was not in use for long. It may have lost its importance due to the course of the Limes Saxoniae around 810. The castle had only one gate that led to the north. Today the ground monument is also known as Wallberg or Sirksfelder Schanze.de.wikipedia.org/wiki/Sirksfelder_Schanze