Segeberger Kalkberg

The Kalkberg (lit. "chalk mountain") is a 91-metre-high rock in the center of Bad Segeberg. The name is a misnomer as it is not made of limestone (calcium carbonate), but from gypsum (calcium sulfate).

The gypsum was formed as sulfate evaporite sediments, which were deposited about 250 million years ago by the Zechstein Sea. Smaller disturbances in the more recent epochs of earth history allowed the less dense Zechstein salts to flow together and force their way upwards from a great depth into the younger overlying rocks to a level near that of the present-day surface. Under the Kalkberg is a salt dome, which rises by one to two millimeters a year. The red cliffs of Heligoland or the Münsterdorfer Geestinsel are limestone, one of the few formations in Schleswig-Holstein which was not created by the ice ages. The mining of the salt dome ended in 1860. From the salt dome comes the brine feeding the saltwater bath that give Bad Segeberg its name.

Originally, the Kalkberg was about 110 m high. After centuries of mining of the gypsum, it stands only 91 meters today. In the Middle Ages, Lothair of Saxony built Siegburg Castle on the mountain - then called Alberg'. The Counts of Schauenburg and Holstein established twice a secundogeniture seated on the Siegburg Castle. The secundogeniture was called County of Stormarn, or Holstein-Segeberg after its mother line and the capital.

Between 1273 and 1308 Adolphus V the Pomeranian, second-born brother of Count John II the One-Eyed of Holstein-Kiel, resided on the castle. Adolphus V was succeeded by John's second-born son Adolphus VII, ruling 1308 to 1315. In 1315 Adolphus VII was slain on Siegburg Castle in his bed by a group of knights led by Hartwig Reventlow personally at feud with him. Holstein-Segeberg was then reincorporated into Holstein-Kiel, itself merged into Holstein-Rendsburg in 1390.

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