On 22 July 1227 a coalition of north German princes and the city of Lübeck beat Valdemar II of Denmark at Bornhöved in Holstein, ending the Danish empire that had held the southern Baltic coast for a quarter of a century and fixing the Danish frontier at the Eider.
The Battle of Bornhöved was fought in Holstein on 22 July 1227 between Valdemar II of Denmark and a coalition of north German princes and towns led by Adolf IV of Holstein. It settled the ownership of the southern Baltic coast for the rest of the Middle Ages. Denmark had held Holstein, Hamburg, Lübeck, Mecklenburg and Pomerania since the first years of the century; after Bornhöved it held none of them, and the Danish frontier came back to the river Eider, where it stayed until 1806.
The battle is unusual in that the losing king had already signed away what he was fighting for. Valdemar had been abducted in 1223 by Count Henry of Schwerin, one of his own vassals, and had bought his release in 1225 by renouncing every German land he held. He then obtained papal absolution from an oath sworn in captivity and marched to take it all back. Bornhöved decided whether a treaty extracted from a prisoner would stand, and it did.
Between 1201 and 1219 Valdemar II turned Denmark into the dominant power of the Baltic. He took Holstein from the Schauenburg counts in 1201, occupied Hamburg and Lübeck, received the homage of the Wendish princes of Mecklenburg and Pomerania, and in 1214 got a golden bull from Frederick II conceding everything north of the Elbe and the Elde. In 1219 he crossed to Estonia, won at Lyndanisse and founded the castle that became Reval. Danish lordship ran round three sides of the sea.
It was an empire of overlordships rather than of administration, and that was its weakness. Valdemar ruled Holstein through a resentful dispossessed comital family, Lübeck through a city that wanted its own trade, and Mecklenburg through princes whose loyalty was personal and temporary. None of it was held by garrisons in the way the crusading orders held Livonia. It needed the king to be present, solvent and credible, and in 1223 he abruptly stopped being any of the three.
On the night of 6–7 May 1223 Valdemar and his eldest son were hunting on the small Danish island of Lyø, without a bodyguard, as the guests of Count Henry I of Schwerin. Henry had a grievance: he had returned from a pilgrimage to find part of his county in the king’s hands and his claim on the rest ignored. He seized both Valdemars, shipped them to Germany, and held them first at Lenzen, then in the tower at Dannenberg, and finally at Schwerin itself. It is one of the very few medieval cases of a reigning king taken prisoner by his own vassal in peacetime.
Denmark and Pope Honorius III both demanded his release and neither got it, because Henry had the backing of the princes who wanted the Danish position broken: Adolf IV of Holstein, Archbishop Gerhard II of Bremen and Henry Borwin II of Mecklenburg. While the king sat in a tower his empire came apart. A Danish army sent to restore the position in the north was beaten at Mölln in January 1225.
The treaty that freed him, sworn at Bardowick late in 1225, was correspondingly brutal: 45,000 marks of silver, the surrender of every claim between the Eider and the Elbe, the renunciation of his overlordship over the German princes except in Rügen, and three of his sons left behind as hostages. Valdemar was released, appealed to Rome that an oath taken in prison did not bind him, was absolved, and reopened the war in 1226.
The campaign of 1227 went well at first — the Danes had the better of the fighting around Rendsburg in 1226 — and in July Valdemar moved south into Holstein against Adolf IV, who had already recovered most of his county. The coalition army marched out of Lübeck and met him near the village of Bornhöved on 22 July.
The fighting was long and, by every account, exceptionally bloody; the later Lübeck chroniclers say the combatants fought knee-deep in blood, which is a formula rather than an observation but carries the memory of a grinding engagement rather than a rout. Valdemar had the larger force and was winning until the Dithmarschen contingent — peasant levies from the marshes who owed him nothing beyond the moment — changed sides in the middle of the battle and turned on the Danish flank.
That decided it. The Danish line broke, Valdemar had several horses killed under him and lost an eye, and he escaped only because his household got him off the field. Otto the Child, duke of Brunswick-Lüneburg and his chief German ally, was captured, as was the bishop of Ribe. The king reached Denmark with an army that no longer existed as a fighting force.
The 22nd of July is the feast of Mary Magdalene, and Lübeck decided that the saint had won the battle. The story that grew up in the city held that a cloud or a sudden blaze of sunlight blinded the Danes while leaving the Germans able to see, and that the Magdalene had appeared to the army as it knelt before the fighting. The date became a civic festival, kept annually in a town whose independence was reckoned to date from that afternoon.
The legend was painted where the city governed itself. Four of the fifteen wall paintings in the Hörkammer of Lübeck’s town hall, made before 1444, showed the Magdalene and the battle; most are now covered or destroyed, though their inscriptions survive. It is a useful reminder of what Bornhöved meant to the winners: not a frontier adjustment, but the moment a merchant city stopped belonging to a king.
Valdemar did not try again. The Danish-German border returned to the Eider and stayed there for close to six centuries; Holstein went back to Adolf IV, and Dithmarschen kept a practical independence it defended for another two hundred and fifty years. Of the whole southern Baltic empire, only the principality of Rügen remained Danish. The king turned inward and spent his last years on law and administration, issuing the Code of Jutland in 1241, the year he died — a legal monument that outlasted the empire by centuries and was Denmark’s law until 1683.
The winners gained more than the loser lost. Lübeck, declared a free imperial city by Frederick II in 1226 and now beyond Danish reach, was left free to organise the Baltic trade on its own account, and it became the leading city of the Hanseatic towns; the Wendish ports of Rostock, Wismar and Stralsund followed it. Adolf IV kept the vow he had made during the fighting: he founded religious houses, entered a Franciscan friary in 1238, was ordained priest at Rome in 1244, and died a friar at Kiel in 1261.
For the Baltic as a whole, Bornhöved moved the initiative from kings to corporations. The sea’s next century belonged to the German merchant cities and to the crusading orders in Prussia and Livonia rather than to a Danish crown — a shift visible nine years later at Saule, where a crusading army that included pilgrims from Holstein was destroyed by the Samogitians.