his siblings were reportedly informed of their father's fate by an envoy from Ælla. As he heard the news, Sigurd was supposedly so affected that he cut himself to the bone with a knife he held in his hand; his brother Björn Ironside supposedly gripped a spear so tightly that the imprint of his fingers was left in the wood. Sigurd and his brothers swore they would avenge Ragnar's death. In 865–866, the Viking leaders Ivar the Boneless and Ubbe crossed the North Sea with a stor hær ("Great Army"). Traditional accounts claim that all the surviving sons of Ragnar apart from Ivar launched a first attack on Ælla's kingdom, which failed. Sigurd's brother, Ivar the Boneless, devised a strategy in which the Great Heathen Army occupied and sacked York, to provoke Ælla into engaging on the Vikings' terms. Under Ivar's plan, the Vikings feigned retreat, leading Ælla to underestimate them and become encircled. According to Ragnarssona þáttr (The Tale of Ragnar's Sons, part of the Sagas of Ragnar Lothbrok), Ælla was captured alive and executed afterwards by blood eagle. Sigurd's descendants Ragnarssona þáttr states that when his father died, Sigurd inherited Zealand, Scania, Halland, the Danish islands, and Viken. It is also possible he was for a time co-ruler of Denmark with his brother Halfdan, because Frankish sources mention certain Sigfred and Halfdan as rulers in 873 – the names Sigurd and Sigfred were often mixed up in Nordic literature. He could have succeeded his brother Halfdan Ragnarsson as the sole king of Denmark in about 877, when Halfdan fell in battle in the Irish Sea. A Danish Viking king called Sigfred, who appears to have become landless by this time, was killed in West Francia in 887; he is quite possibly the same person. Sigurd married Blaeja, the daughter of king Ælla of Northumbria and they had two children, Harthacanute and Áslaug Sigurðardóttir, who was married to Helge of the Dagling lineage. Helge may have briefly succeeded his purported father-in-law as king of Denmark before being overthrown by Olof, a Viking chief who swept down from Sweden in about the year 900. The Ragnarssona þáttr states that Danish king Harthacanute was a son of Sigurd. However, the 11th century chronicler Adam of Bremen mentions Hardegon (probably Harthacanute) as the son of a certain Sven. Hardegon or Harthacanute succeeded Sigtrygg Gnupasson as the king of part of Denmark (probably