by Susan Flantzer
© Unofficial Royalty 2025

Born circa 1042, King Cnut IV of Denmark was the second of five illegitimate sons of Sweyn II Estridsson, King of Denmark to become King of Denmark. He reigned from 1080 until 1086, when rebels killed him. Cnut was canonized as a saint by the Roman Catholic Church, and in 110,  the Roman Catholic Church recognized him as the patron saint of Denmark.

Cnut’s 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.

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 Cnut’s full siblings or half-siblings. “Brother” will be used when discussing Cnut’s male siblings but it is unknown whether they were full brothers or half-brothers.

• 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
• Olaf I, King of Denmark (circa 1050 – 1095)
• Eric I Evergood, King of Denmark (circa 1056 – 1103)
• Svend Tronkræver (? – 1104)
• Ulf Svendsen (Ubbe) (? – 1104)
• Benedict Svendsen (? – 1086)
• Bjørn Svendsen, Duke of Nordalbingien (circa 1062 – 1100)
• Niels, King of Denmark (circa 1065 – 1134)
• 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 1082, Cnut married Adela of Flanders (circa 1064 – 1115), daughter of Robert I, Count of Flanders and Gertrude of Saxony. The marriage was part of an alliance between Flanders and Denmark against King William I of England (the Conqueror). Cnut and Adela had three children, a son and twin daughters:

• (Blessed) Carl the Good, Count of Flanders (1084 – 1127), killed in Saint Donatian Church in Bruges, County of Flanders, now in Belgium by a conspiracy of the rich whom he had offended, beatified in 1883
• Cecilia Knudsdatter of Denmark (circa 1081 – 1085 – after January 7, 1131), married Erik, Earl of Västergötland, later became Earl of Falster, had two sons and one daughter
• Ingegerd Knutsdatter of Denmark (circa 1081 – 1085 – ?), married Folke the Fat of Sweden, had two sons

When Cnut’s father Sweyn II Estridsson, King of Denmark, died in 1076, there were two candidates for the Danish throne, Harald, Sweyn II’s eldest illegitimate son, and Cnut, Sweyn II’s second illegitimate son. An assembly of Danish nobles had to choose between the two candidates. Harald was seen as more peaceful, while Cnut wanted to reconquer England. To convince the nobles to vote for him, Harald took the vows called Harald’s Laws, declaring that he would uphold the existing rule of law. Cnut was sent into exile and did not return until his brother, King Harald III of Denmark, died in 1080, when Cnut succeeded his childless brother as King Cnut IV of Denmark.

The reign of King Cnut IV of Denmark focused on three areas: his desire to strengthen the Danish monarchy, his deep religious devotion and strong support of the Roman Catholic Church, and his desire to be the King of England. Cnut IV attempted to increase his royal power by stifling the nobles and their power. His policies and actions led to discontent among his subjects and are considered a direct cause of his eventual murder.

Cnut issued edicts giving the king ownership of common lands, rights to the goods on shipwrecks, and the right to inherit the property of foreigners and those without descendants. During Cnut’s reign, Denmark was still Roman Catholic and would remain so until the Protestant Reformation, when Lutheranism became Denmark’s official religion in 1536. Cnut enhanced the Roman Catholic Church’s authority by establishing stricter penalties for offenses committed on church holidays and enforcing the collection of tithes, giving ten percent of one’s income to the church. Cnut gave large sums of money to the churches in Dalby, Luns, Odense, Roskilde, and Viborg. Cnut’s actions made the Roman Catholic Church in Denmark a powerful ally, and in turn, the church supported Cnut’s position of power.

As the great-grandson of Cnut the Great, King of England, Denmark, and Norway, King Cnut IV believed he was entitled to the English crown and saw William the Conqueror, now King William I of England, as a usurper. In 1085, Cnut planned an invasion of England with the support of his father-in-law, Robert I, Count of Flanders and King Olaf III of Norway. However, the invasion never happened because Cnut feared an invasion of Denmark’s southern border by Heinrich IV, Holy Roman Emperor.

The Danish fleet with the Danish army aboard the ships remained in Danish ports. Supplies were running low, and the harvest was approaching. A council was held, and Cnut’s half-brother Olaf, the future King Olaf I of Denmark, was sent to ask him to begin the English campaign or send the army home. Cnut feared Olaf’s support among the nobles. Olaf had concerns about Cnut’s ambitions and saw Cnut’s young son Carl, born the previous year, as a future rival for power. Cnut blamed Olaf for stirring up trouble, and Olaf was imprisoned by their brother Eric, the future King Eric I of Denmark. Olaf was banished to Flanders, under the supervision of Robert I, Count of Flanders, Cnut’s father-in-law.

However, Cnut’s actions resulted in open rebellion. He had to flee from the royal estate in Børglum and continued to flee to Aggersborg,  Viborg, and Schleswig, finally ending up in Odense. On July 10, 1086, Cnut, his brother Benedikt, and seventeen of their followers took refuge in the wooden, Viking Age St. Alban’s Priory Church (link in Danish) at St. Alban’s Priory in Odense. The rebels stormed into the church and killed Cnut, his brother Benedikt, and their seventeen followers before the altar. The Benedictine monks of St. Alban’s Priory buried Cnut and his brother Benedikt in front of the main altar of the St. Alban’s Priory Church.

Cnut was considered a martyr, and calls for his canonization as a saint were quickly heard. During the reign of Cnut’s brother and successor, King Olaf I of Denmark, Denmark suffered from crop failure. This was seen as divine retribution for Cnut’s murder. There were reports of miracles occurring at his burial site, and his canonization was already being sought during King Olaf I of Denmark’s reign (1086 – 1095). In 1101, persuaded by King Eric I of Denmark (reigned 1095 – 1103), brother of King Cnut IV and successor of their brother King Olaf I of Denmark, Pope Paschal II canonized King Cnut IV as a saint in the Roman Catholic Church.

Soon after Cnut’s murder, construction began on the first Saint Cnut’s Cathedral, just southwest of St. Alban’s Priory Church in Odense, Denmark. In 1095, construction had progressed enough for Cnut’s remains to be transferred from St. Alban’s Priory Church to the crypt at Saint Cnut’s Cathedral. The new cathedral was completed in 1122 and consecrated in Cnut’s name. In 1247, a fire devastated Odense, and the cathedral was badly damaged.

In 1280, construction began in Odense, Denmark on the second and current Saint Cnut’s Cathedral in the Brick Gothic style. By 1300, construction had progressed enough to allow the reburial of Cnut IV, King of Denmark, and his brother Benedikt in the cathedral’s crypt. It took more than 200 years to complete the second cathedral, which was dedicated on April 30, 1499. Originally Roman Catholic, Saint Cnut’s Cathedral has been Evangelical-Lutheran since the Danish Reformation. The remains of Cnut and Benedikt were walled up by the monks in an alcove in the cathedral to protect the remains from destruction during the Danish Reformation.  During the 19th century, their long-forgotten coffins were discovered, and the remains of Cnut and his brother Benedikt are now on display in the cathedral.

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Works Cited

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