Dithmarschen (ˈdɪtmaʁʃn̩, Low Saxon: ˈdɪtmaːʃn̩; archaic English: Ditmarsh; Ditmarsken; Tedmarsgo) is a district in Schleswig-Holstein, Germany. It is bounded by (from the north and clockwise) the districts of Nordfriesland, Schleswig-Flensburg, Rendsburg-Eckernförde, and Steinburg, by the state of Lower Saxony (district of Stade, from which it is separated by the Elbe river), and by the North Sea. From the 13th century up to 1559 Dithmarschen was an independent peasant republic within the Holy Roman Empire and a member of the Hanseatic League. The district is located on the North Sea. It is embraced by the Elbe estuary to the south and the Eider estuary to the north. Today it forms a kind of artificial island, surrounded by the Eider river in the north and the Kiel Canal in both the east and southeast. It is a rather flat countryside that was once full of fens and swamps. To the north it borders on Nordfriesland and Schleswig-Flensburg, to the east on Rendsburg-Eckernförde, and in the southeast on Steinburg. Its landward boundaries have remained basically the same since the times of Charlemagne. Land reclamation, however, has almost doubled the size of Dithmarschen as land has been wrested from the sea. The main roads and rail lines in Schleswig-Holstein follow a north–south direction, making Hamburg its most accessible city. The district has a maximum north–south length of 54 kilometers and an east–west length of 41 kilometers. The highest point, near Schrum in the geestland, is meters above sea level and the lowest point, near Burg, is below sea level. Dithmarschen's landscape owes its character to the North Sea. From west to east Dithmarschen consists of the Wadden Sea, marsh, bog, and the geestland. The North Sea had a higher sea level 6,500 years ago than today and the coastline then ran along the geestland. About 4,500 years ago, geestland structures were connected by sand and gravel depositions that formed spits. Bogs, lakes, and swamps emerged as the area behind the spits no longer flooded.