Björn (Old Norse: Bjǫrn) was a Swedish monarch or local ruler who ruled over Birka, an important port town, and possibly Uppsala, an important early Swedish political center, around the year 829. His existence is attested by the nearly contemporary account Vita Ansgari, written by the missionary Rimbert, who visited Sweden alongside Ansgar in 852. He is in fact the first Swedish figure referred as king who is known from a reasonably reliable source. Older Swedish historiography often identified the king with the legendary figure Björn at Haugi, who was supposedly a Swedish ruler in the generation before the youth of Harald Finehair of Norway. This identification is however considered unverifiable, since Björn at Haugi may have actually been a Norwegian local ruler who was later constructed as a Swedish king. Although the genealogy of early Swedish local rulers is not known, Björn is assumed to have belonged to the House of Munsö, which would later produce Eric the Victorious, generally considered to be Sweden's first king. The royal names attested in the ninth century, namely, also occur among the kings and princes in the late Viking age, perhaps suggesting a genealogical continuity. Rimbert's account Ansgar had previously worked in Denmark with the consent of King Harald Klak, a protégé of Emperor Louis the Pious. In 829, Swedish ambassadors arrived to the court of Louis in Worms. Among other matters they told the Emperor that many people in their country wished to embrace the Christian religion, and that their king endorsed the arrival of proper teachers. The Emperor summoned Ansgar and ordered him to go the land of the Swedes and investigate whether people were indeed prepared to accept Christianity. Thus Ansgar tread the journey together with his companion Witbert, sailing with a party of merchants. When about half-way, the ships were attacked by Vikings and those on board had to save themselves on shore. The missionaries lost the gifts and possessions they had carried, but nevertheless decided to proceed. After traveling a long distance, mostly by foot, they arrived to the port of the kingdom which was called Birka, where they were friendly received by the king, whose name was Björn ("Tandem ad portum regni ipsorum, qui Byrca dicitur, pervenerunt, ubi benigne a rege, qui Bern vocabatur, suscepti sunt"). Some scholars have called Björn "king of Birka", but this has no foundation in Rimbert's writings, as Rimbert merely writes