Danish March

The terms Danish March and March of Schleswig (German: Dänische Mark or Mark Schleswig) are used to refer to a territory in modern-day Schleswig-Holstein north of the Eider and south of the Danevirke. It was established in the early Middle Ages as a March of the Frankish Empire to defend against the Danes. The term "Danish March" is a modern designation not found in mediaeval sources. According to the Royal Frankish Annals the Danish King led his troops "into the March" in 828 (ad marcam). In the 852 Yearbook of Fulda there is mention of a "Guardian of the Danish Border" (custodes Danici limitis).

In Old Norse, Denmark was called Danmǫrk, viz. the marches or the Danes. The Latin name is Dania.

Charlemagne is believed to have established a Danish March around 810 CE, following rulership claims by the ambitious Danish King Gudfred over the territory north of the Elbe, which was at the time part of Saxony and which Charlemagne had recently subjugated. The duration and extent of the Carolingian march is however uncertain. In 811 it was agreed that the Eider would mark the Danish southern border. However, in the Royal Frankish Annals of 828 it was recorded that the Danes crossed into the "March" and crossed the Eider, the formulation of which raises the possibility that the Carolingian march lay to the north of the Eider.

In Wigmodi (a Gau which lay between the mouths of the Elbe and the Weser) and in Nordalbingia (north of the Elbe) the Saxons had resisted Charlemagne for the longest. Many of the rebelling Nordalbingians were deported to the interior of the Frankish Empire in 795 and especially 804 with their lands initially being left to the Slavic Obotrites to act as a buffer between the Franks and the Danes. After the Obotrites were forced to become Danish tributaries in 808, the Franks crossed the Elbe again and according to the Royal Frankish Annals began construction of Esesfeld Castle on 15 March 809.

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