The saga Ragnarssona þáttr relates the acts of the sons of Ragnar Lodbrok, and proceeds to link them genealogically to the later rulers of the Scandinavian kingdoms. For Denmark, it relates that by Blaeja, the daughter of King Ælla of Northumbria, Sigurd Snake-in-the-Eye became father of Harthacnut. Harthacnut is said to have been his father's successor in Zealand, Scania and Halland, but not the break-away Viken, and he was father of Gorm. Scholarly opinion is divided as to the degree to which the material found in such heroic sources is to be taken as authentic history and genealogy.
''Gesta Hammaburgensis ecclesiae pontificum'' of Adam of Bremen
Two possible references to Harthacnut appear in the work of clergyman Adam of Bremen, who came from Germany to record the history of the Archbishops of Bremen, partly based on information from Gorm's descendant, Sweyn II of Denmark. Adam states that a king Helge was deposed and Denmark was conquered by Olof the Brash who came from Sweden. Along with two of his sons, Gyrd and Gnupa, Olof took the realm "by force of arms," and they ruled it together, thus founding the House of Olaf in Denmark. Adam reports that they were followed by a Sigtrygg. That Sigtrygg was the son of Gnupa by a Danish noblewoman named Asfrid, is shown on two runestones near Schleswig, erected by his mother after his death. Adam then relates that after Sigtrygg reigned a short time, during the tenure of Archbishop Hoger of Bremen, Hardegon, son of Sweyn, came from "Northmannia" the "land of the Northmen," by which he may have meant Norway, Normandy, which had recently been colonized by Danish Vikings, or even northern Jutland. Hardegon immediately deposed the young king Sigtrygg, and then ruled unopposed for approximately thirty years. Hardegon is often equated with the Harthacnut of legend, but some historians, such as Lis Jacobsen, instead have concluded that Hardegon is distinct. Adam later refers to an attack on Denmark by Henry I of Germany, naming the defending king as Hardecnudth Vurm in some manuscripts,filius Hardecnudth Vurm in others. Historians generally agree that Vurm is a German rendering of the Danish name Gorm, and this leads to alternative interpretations, that this is reference to Gorm, son of Harthacnut, or that it is a double-name indicating that Harthacnut and Gorm were the same person. The Saxon chronicles of Widukind of Corvey reports the defeat and forced baptism of the Danish kingChnuba, in 934 at the hands of German king Henry. Likewise, Olav Tryggvasson's Saga tells of Gnupa's defeat by Gorm the Old. Some historians have taken these as indications that Sigtrygg's father Gnupa still ruled at least part of Denmark much later than credited by Adam of Bremen, and his dynasty was only displaced by Harthacnut's son, Gorm.
In the late and legend-influenced Gesta Danorum of Saxo Grammaticus, Harthacnut appears as Knut. He is described as a son of Erik, a descendant of Ragnar Lodbrok, by Gudorm, the granddaughter of Harald Klak. In his version of the tale, Harthacnut is raised by Ennignup, but never accepts Christianity.
Silverdale treasure
In the Silverdale Hoard is a silver coin impressed with the name "Airdeconut" an Anglicized variant of Harthacnut. The hoard dates to the early 10th century, but the style is similar to coins of other viking kings of Northumbria. Thus there is no reason to suggest this coin relates to a king Harthacnut of Denmark rather than an otherwise unknown Northumbrian viking. However, some have suggested that Northumbria may be the Northmannia from which Adam's Danish conqueror Hardegon came.
