by Susan Flantzer
© Unofficial Royalty 2025

Born circa 1065, Niels, King of Denmark from 1104 to 1134, was the fifth of five illegitimate sons of Sweyn II Estridsson, King of Denmark to become King of Denmark. Niels’ father, Sweyn II, married twice. His first marriage was childless. According to the chronicle “Jerusalem History”, Sweyn the Crusader, the legitimate son of a King of Denmark, took part in the First Crusade, dying in battle in 1097. Some researchers believe that he was the son of Sweyn II from his second marriage, but there is no documentary evidence of the existence of Sweyn the Crusader. Sweyn the Crusader would have been living when Sweyn II died in 1076. It would seem logical that a legitimate son of Sweyn II would have been considered a candidate to be his successor. However, only his illegitimate sons Harald III, Sweyn II’s successor, and Cnut IV, who succeeded Harald III, were considered.

Portrait of King Sweyn II that marks his place of burial in Roskilde Cathedral; Credit – Wikipedia

Sweyn II had many mistresses and fathered at least twenty children. The identity of the mothers of his illegitimate children is uncertain. Sweyn II’s illegitimate children, listed below, are either Niels’ full siblings or half-siblings. “Brother” will be used when discussing Niels’ male siblings, but whether they were full brothers or half-brothers is unknown.

• Knud Magnus (circa 1041 – 1058) – King Sweyn II wanted his eldest son Knud Magnus crowned as his successor by the Pope, but Knud Magnus died on the journey to Rome
• Harald III, King of Denmark (circa 1042 – 1080) was King of Denmark from 1076 to 1080
• Saint Cnut IV, King of Denmark (circa 1042 – 1086) was King of Denmark from 1080 to 1086
• Olaf I, King of Denmark (circa 1050 – 1095)
• Eric I, King of Denmark (circa 1056 – 1103)
• Svend Tronkræver (? – 1104)
• Ulf Svendsen (Ubbe) (? – 1104)
• Benedict Svendsen (? – 1086)
• Bjørn Svendsen, Duke of Nordalbingien (circa 1062 – 1100)
• Sigrid Svendsdatter (? – after 1066), married (Saint) Prince Gottschalk, who established the Polabian Slavic kingdom in present-day northeastern Germany
• Ingerid Svendsdatter (? – after 1093), wife of King Olav III of Norway
• Thorgils Svendsen
• Sigurd Svendsen, died in the war against the Wends
• Guttorm Svendsen
• Ømund Svendsen
• Ragnhild Svendsdatter, wife of Svein Aslaksson

In 1105, Niels married Margareta Fredkulla, daughter of King Inge the Elder of Sweden and Queen Helena.  Margareta had been married before. In 1101, she married King Magnus III of Norway. The marriage had been part of the peace treaty between Sweden and Norway. After two years of a childless marriage, King Magnus III died, and Margareta returned to Sweden.

Niels and Margareta had two children:

Niels’ brother King Eric I announced that he would go on a pilgrimage to the Holy Land. King Eric I and his wife Queen Bodil traveled with a large entourage via Novgorod, Russia, to Constantinople, then the capital of the Byzantine Empire, now the city of Istanbul in Turkey. In Constantinople, Eric and Bodil were received by the Byzantine Emperor Alexios I Komnenos. However, Eric never made it to the Holy Land. While in Constantinople, Eric became ill, but despite his illness, he continued his travels by sea. King Eric I of Denmark died on July 10, 1103, in Paphos, Cyprus, where his wife had him buried. King Eric I had chosen Harald Kesja (1080 – 1135), one of his illegitimate children, as his successor, but when the nobles met, they chose Niels to be the next King of Denmark.

During King Niels’ early reign, a positive relationship developed between the Danish government and the Roman Catholic Church in Denmark, led by Asser Thorkilsen, Archbishop of Lund. Niels was the first Danish monarch to use the term “King by the Grace of God”. He limited the size of his entourage, reducing traveling costs. Niels appointed officials throughout Denmark whose responsibility was collecting fines, seizing the cargo of shipwrecks, and confiscating inheritances that went to the crown if there was no heir.

In 1130, King Niels’ wife Margareta died. The land she owned in Sweden became a base for her son Magnus. When Margareta’s first cousin, King Inge the Younger of Sweden, died circa 1125, Magnus claimed the Swedish throne as the eldest grandson of King Inge the Elder and reigned as King Magnus I of Sweden.

After Maragreta’s death, King Niels married Ulvhild Håkansdotter, the daughter of the Norwegian noble Haakon Finnsson. She had first married Margareta’s first cousin, King Inge the Younger of Sweden, but they had no children. Niels and Ulvhild also had no children. After Niels died in 1134, Ulvhild married King Sverker I of Sweden, and they had at least two surviving sons and two surviving daughters.

Niels’s nephew Saint Cnut Lavard, King Eric I’s son; Credit – Wikipedia

In 1115, King Niels of Denmark created his nephew Cnut Lavard (the legitimate son of Niels’ brother King Eric I), Earl of Schleswig. Cnut Lavard used the title Earl of Schleswig for just a short time before he began to style himself Duke of Schleswig. He was the first of many Dukes of Schleswig, and the first border prince who was both a Danish and a German vassal. In 1131, Cnut Lavard was killed by his cousin, King Niels’ son Magnus, who saw Cnut Lavard as a rival to the Danish throne. Cnut Lavard was canonized as a saint by the Roman Catholic Church in 1170. The murder of Cnut Lavard started several years of civil war between King Niels and his son Magnus against Cnut Lavard’s illegitimate half-brother Eric Emune, the future Eric II, King of Denmark.

The civil war between the family members culminated on June 4, 1134, when the two sides fought the Battle of Fodevig near Lund in Scania, now in Sweden. The battle was a decisive victory for Eric Emune, who became the next King of Denmark as Eric II. Magnus was killed in battle, and King Niels fled to Schleswig, where the citizens avenged Cnut Lavard, their beloved Duke of Schleswig, by murdering Niels on June 25, 1134.

The Schlei, where local fishermen retrieved Niels’ body; Credit – By Frank Maahs – Selbst erstellt von Frank Maahs, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2746723

King Niels’ headless body was pulled out of the Schlei, a narrow inlet of the Baltic Sea, by local fishermen. The body was laid out in St. Peter’s Cathedral, then in the Duchy of Schleswig, now in Schleswig, Germany. The monks at the cathedral heard strange noises and thought Niels’ spirit was wandering in the cathedral. As a result, Niels’ body was instead buried in “a boggy grave”. A stake was hammered through Niels’ chest to keep him there. There are local legends that King Niels haunts St. Peter’s Cathedral and hunts the moors of Schleswig with his hounds.

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Works Cited

• Flantzer, Susan. (2025). Eric I, King of Denmark [Review of Eric I, King of Denmark]. Unofficial Royalty. https://www.unofficialroyalty.com/eric-i-king-of-denmark/
• Flantzer, Susan. (2025). Sweyn II Estridsson, King of Denmark. Unofficial Royalty. https://www.unofficialroyalty.com/sweyn-ii-estridsson-king-of-denmark/
• Bidragsydere til Wikimedia-projekter. (2003). Niels, Konge af Danmark. Wikipedia.org; Wikimedia Foundation, Inc. https://da.wikipedia.org/wiki/Niels_af_Danmark
• Ulvhild Håkansdotter [Review of Ulvhild Håkansdotter]. (2025). Wikipedia. https://en.wikipedia.org/wiki/Ulvhild_H%C3%A5kansdotter
• Wikipedia Contributors. (2025). Canute Lavard. Wikipedia; Wikimedia Foundation.
• Wikipedia Contributors. (2025). Eric I of Denmark. Wikipedia; Wikimedia Foundation.
• Wikipedia Contributors. (2025). Niels of Denmark. Wikipedia; Wikimedia Foundation.
• Wikipedia Contributors. (2025). Schleswig Cathedral. Wikipedia; Wikimedia Foundation.