King John of Denmark, at that time also king of the Kalmar Union, had a problem on his southwestern flank. The marshland of Dithmarschen, between the Eider and the Elbe, had governed itself for generations as a peasant republic with no lord and no intention of acquiring one. John and his brother Duke Frederick, co-dukes of Schleswig and Holstein, decided in the winter of 1500 to settle the matter. They assembled something like twelve thousand men: the Black Guard - the Schwarze Garde - under a minor nobleman named Thomas Slentz, some two thousand armoured cavalry drawn largely from the Holstein nobility, roughly a thousand artillerymen, and thousands of levied commoners. The campaign opened on 11 February. Meldorf fell, and the column turned north along the raised road toward Heide and Lunden. On paper the outcome was not in question.

The Dithmarschers could put at most six thousand men in the field, all of them farmers, under a leader named Wulf Isebrand. What they had instead of professionals was the ground, and an exact knowledge of what it would do if you asked it. South of Hemmingstedt, at a spot called Dusendduewelswarf, they threw a palisade across the causeway at right angles and mounted guns behind it. Then they opened the dike sluices. February had brought a thaw. Meltwater, rain and seawater came into the fields on either side of the road, and within hours the marsh had turned into a shallow lake over bottomless mud. There was now exactly one place the Danish army could stand, and it was a narrow ribbon of road with a fortified wall at the end of it.

The Black Guard went at the palisade and tried to work around its flanks, which meant leaving the road. Men in three-quarter armour, carrying pikes designed for open ground, stepped off the causeway into water and silt and stopped being soldiers. Behind them the column could not deploy; the artillery could not be brought forward; the cavalry could not charge. The Dithmarschers came at them barefoot and lightly armed, vaulting the drainage ditches on long poles, knowing which strips of ground would hold a man's weight and which would not. Slentz was killed. The fighting lasted about three hours before the Guard broke, and when it broke the levies and the horsemen behind it broke too. Most of the men who died that day were not killed by a weapon. They drowned, in cold water, in armour, within sight of a road they could not reach. Afterwards the Dithmarschers buried the enemy's common soldiers, but in their contempt for the nobility they left the bodies of the noblemen where they lay in the fields.

The traditional figures are enormous and should be treated with care. Older accounts have the invading army losing more than half its strength - some seven thousand killed and fifteen hundred wounded. Contemporary claims put the Danish dead nearer four thousand, along with noblemen of the Holstein and Oldenburg houses. Every one of those numbers comes from the winners. The historian Walther Lammers made the sceptic's decisive point: an army of that size on a single causeway would have stretched close to ten kilometres, meaning a substantial part of it was still in and around Meldorf while the front collapsed and never fought at all. Dithmarschen's own losses went untallied by contemporaries; one modern estimate puts them around sixty dead, though that figure too rests on thin evidence. What is not in doubt is the scale of the defeat, or its cause. The peace treaty of 15 May 1500 left the peasant republic intact.

Among the trophies was the Dannebrog itself, the Danish royal banner, carried into the battle by Hans von Ahlefeldt. It hung in St. Nicholas Church at Woehrden for nearly sixty years, until Frederick II of Denmark finally conquered Dithmarschen in the Last Feud of 1559 and demanded it back. The Dithmarschers had also vowed a monastery to Mary of Nazareth if they survived, and in 1513 they made good on it with a Franciscan friary at Lunden. Then the storytelling began. A maiden called Telse was said to have carried the Marian banner into the fighting; a farmer named Reimer von Wiemerstedt was credited with killing Slentz. Neither can be shown to have existed, which did not stop Max Friedrich Koch from painting Telse and her banner across a wall of the district building in Meldorf in 1910. A monument went up at Dusendduewelswarf in 1900, on the four hundredth anniversary, at the height of German-Danish nationalism, and the Nazi party later mined the battle hard for propaganda about free Germanic peasant warriors. A quieter information pavilion now stands on the site, telling the story with the mythology labelled as such.