Southern Jutland (Danish: Sønderjylland; German: Südjütland) is the region south of the Kongeå in Jutland, Denmark and north of the Eider (river) in Schleswig-Holstein, Germany. The region north of the Kongeå is called Nørrejylland, 'Northern Jutland'. Both territories had their own ting assemblies in the Middle Ages (in Viborg and Urnehoved). Southern Jutland is mentioned for the first time in the Knýtlinga saga.
In the 13th century South Jutland became a duchy. The first duke was Canute Lavard (Knud Lavard). In the late 14th century, House Schauenburg orchestrated a political coup led by the German prince Gerhard III. One of his most symbolic actions was renaming the duchy. 'South Jutland' was a distinctly Danish term, linking the region to North Jutland and reinforcing its connection to Danish identity and the Kingdom of Denmark. Gerhard aimed to sever these ties and anchor the duchy more firmly within the German cultural sphere. As a result, the region was renamed the Duchy of Schleswig. The new name derived from the city of Schleswig (Slesvig). Naming duchies after their principal cities was a common German ducal practice, as seen in examples such as the Duchies of Brunswick (Braunschweig), Mecklenburg, Magdeburg, Anhalt, and others. The dukes of Schleswig also became kings of Denmark.
