In order to win Astrid, the daughter of the Wendish chieftain Burislav, he promised to liberate the Wends of the tribute they had to pay to the Danes. He fulfilled his promise by sailing to Zealand where he sent the message to Sweyn Forkbeard that he had important tidings, but had fallen ill and could not come in person to bring them to him. As Sweyn was curious, he went aboard Sigvaldi's ship and was captured by the Jomsvikings. To be liberated the Danish king had to grant independence to both the Jomsvikings and to the Wends, in addition to paying a king's ransom. Svein also had to marry Gunhild of Wenden, daughter of Burislav and Burislav married Sweyn's sister Tyri.