Forkbeard, who was the son and heir to King Harald Bluetooth and thus came from a line of Scandinavian rulers central to the unification of Denmark. Neither the place nor the date of his birth are known. Harthacnut I was the semi-legendary founder of the Danish royal house at the beginning of the 10th century, and his son, Gorm the Old, became the first in the official line (the 'Old' in his name indicates this). Harald Bluetooth, Gorm's son and Cnut's grandfather, was the Danish king at the time of the Christianization of Denmark; he became one of the first Scandinavian kings to accept Christianity. The Chronicon of Thietmar of Merseburg and the Encomium Emmae report Cnut's mother as having been Świętosława, a daughter of Mieszko I of Poland. Norse sources of the High Middle Ages, most prominently Heimskringla by Snorri Sturluson, also give a Polish princess as Cnut's mother, whom they call Gunhild, a daughter of Burislav, the king of Vindland. Since in the Norse sagas the king of Vindland is always Burislav, this is reconcilable with the assumption that her father was Mieszko (not his son Bolesław). Adam of Bremen in Gesta Hammaburgensis ecclesiae pontificum is unique in equating Cnut's mother (for whom he also produces no name) with the former queen of Sweden, wife of Eric the Victorious and by this marriage mother of Olof Skötkonung. To complicate the matter, Heimskringla and other sagas also have Sweyn marrying Eric's widow, but she is distinctly another person in these texts, named Sigrid the Haughty, whom Sweyn only marries after Gunhild, the Slavic princess who bore Cnut, has died. Different theories regarding the number and ancestry of Sweyn's wives (or wife) have been advanced (see Sigrid the Haughty and Gunhild). But since Adam is the only source to equate the identity of Cnut's and Olof Skötkonung's mother, this is often seen as an error on Adam's part, and it is often assumed that Sweyn had two wives, the first being Cnut's mother, and the second being the former Queen of Sweden. Cnut's brother Harald was the younger of the two brothers according to Encomium Emmae. Some hint of Cnut's childhood can be found in the Flateyjarbók, a 13th-century Icelandic source that says he was taught his soldiery by the chieftain Thorkell the Tall, brother to Sigurd, Jarl of Jomsborg, and the legendary Jomsvikings, at their stronghold on the island