The long Baltic inlet reaching inland to Schleswig: the waterway that carried Hedeby’s trade, the line the Danevirke defended, and the water in which Eric IV of Denmark was killed in 1250.
The Schlei is a fjord in Schleswig defining the southern boundary of the Danish peninsula near the historic town of Schleswig. The region was historically contested between Danish royal authority and German imperial influence.
It is not a point on a map but a narrow arm of the Baltic running roughly thirty kilometres inland, from the sea at Schleimünde to the town of Schleswig at its head, dividing the peninsula of Angeln to the north from Schwansen to the south. Its Danish name is Slien. Shallow, sheltered and full of small bays, it let a shallow-draught ship sail deep into the land without meeting open sea.
That geography made the head of the Schlei one of the most valuable places in early medieval Europe. Hedeby, at the inlet’s western end, was the greatest trading settlement of the Viking-age north, precisely because it sat at the narrowest part of the Jutland peninsula: goods could be landed there from the Baltic and carried a short way overland to the North Sea rivers, avoiding the long and dangerous passage round Skagen.
The Danevirke, the earthwork rampart that Danish kings extended across the peninsula from the ninth century onwards, met the water at this end. The Schlei was its eastern flank, which is the clearest measure of what the inlet was worth: the Danish crown fortified the whole neck of the peninsula rather than lose the harbour at the top of it.
Hedeby was abandoned in the eleventh century after raiding and fire, and the town of Schleswig on the north bank took over its trade and its name for the region. A bishopric and a ducal residence followed, and the duchy of Schleswig grew up as a Danish fief along the inlet and the land south of it.
The Eider, a short way further south, was the boundary of the Holy Roman Empire. That left the Schlei sitting inside a permanently contested strip: Danish by lordship, German by neighbourhood, and disputed by both for the rest of the Middle Ages, particularly after the duchy passed as a fief to the counts of Holstein in the later fourteenth century.
On 10 August 1250 Eric IV of Denmark, returning from Estonia, accepted his brother Abel’s hospitality at Gottorp on the Schlei. That evening, while the king was playing at dice with a German knight, the duke’s chamberlain broke in with armed men and took him prisoner.
He was bound and carried out to a boat on the inlet. A second boat came after them across the water, and when Eric heard the voice of Lave Gudmundsen in it he understood what was coming. He was beheaded in the boat and his body thrown into the Schlei. Fishermen dragged the headless corpse up in a net the next morning and carried it to the Dominican house at Schleswig; it was moved to Ringsted in 1257. Abel took the throne insisting he had nothing to do with it, and was killed himself within eighteen months.
The Schleswig corridor where the Schlei sits was the focus of repeated political and military conflict between Denmark and the Duchy of Holstein. Margaret I’s operations in the region during the 1380s and 1390s reflected her effort to stabilize the southern border of Danish power as she consolidated the Kalmar Union.
The inlet’s importance had by then changed in kind. It was no longer the artery of a trading emporium but the line along which a frontier was argued over, and it stayed one of the most disputed borders in Europe into the nineteenth century.