There is scant material in medieval chronicles to provide details regarding the marriages of Sweyn of Denmark: •
Thietmar of Merseburg mentions that the daughter of
Mieszko I of Poland and sister of
Bolesław I of Poland married
Sweyn Forkbeard and gave him sons Cnut and Harold, but he does not mention her name. Thietmar is probably the best informed of all medieval chroniclers, since he was contemporary with described events and well-informed about the events in Poland and
Denmark. The assertion that Harald and Cnut's mother was Bolesław's sister may explain some mysterious statements that appear in medieval chronicles, such as the involvement of Polish troops in invasions of England. •
Adam of Bremen writes that a Polish princess was the wife of
Eric the Victorious and by this marriage the mother of
Olof Skötkonung of Sweden. In her second marriage with Sweyn, she became mother of Cnut and Harold of Denmark. Consequently, Adam calls Cnut and Olof brothers. Some historians consider Adam's account unreliable, because he is the only source to state this relationship. •
Gesta Cnutonis regis mentions in one short passage that Cnut and his brother went to the land of the Slavs, and brought back their mother, who was living there. This does not necessarily mean that his mother was Slavic, but nevertheless this chronicle strongly suggests that she was. • There is an inscription in "Liber vitae of the New Minster and Hyde Abbey Winchester", that king Cnut's sister's name was "Santslaue" ("Santslaue soror CNVTI regis nostri"), which without doubt is a Slavic name. J. Steenstrup suggests that Canute's sister may have been named after her mother, hence coining (the now generally agreed upon) hypothesis, that her
Old Polish name is
Świętosława, but only as a reconstruction based on a single mention of her daughter's name and the hypothesis that she named her daughter after herself. ==Identities==