It was not long before a pretext was found for an attack. Thyra, Sweyn's sister, the widow of Styrbjörn, had been married to Mieczislav, the Duke of Poland. In 992, she was widowed the second time. After a few years, perhaps in 998, Olaf Trygvesson made her queen of Norway. Later events would indicate that this marriage, which Olaf seems to have contracted without consulting the bride's brother, was part of a plan to unite against Sweyn all the forces that were presumably hostile,—Poles, Jomvikings, and Norsemen.[48]
The saga writers, keenly alive to the influence of human passion on the affairs of men, emphasise Sigrid's hatred for Olaf and Thyra's anxiety to secure certain possessions of hers in Wendland as important causes of the war that followed. Each is said to have egged her husband to the venture, though little urging can have been needed in either case. In the summer of 1000, a large and splendid Norwegian fleet appeared in the Baltic. In his negotiations with Poles and Jomvikings, Olaf was apparently successful: Sigvaldi joined the expedition and Slavic ships were added to the Norse armament. Halldor the Unchristian tells us that these took part in the battle that followed: "The Wendish ships spread over the bay, and the thin beaks gaped with iron mouths upon the warriors."[49]
Sweyn's opportunity had come and it was not permitted to pass. He mustered the Danish forces and sent messages to his stepson in Sweden and to his son-in-law Eric. Sigvaldi was also in the alliance. Plans were made to ambush the Norse King on his way northward. The confederates gathered their forces in the harbour of Swald, a river mouth on the Pomeranian coast a little to the west of the isle of Rügen. Sigvaldi's part was to feign friendship for Olaf and to lead him into the prepared trap. The plan was successfully carried out. A small part of King Olaf's fleet was lured into the harbour and attacked from all sides. The fight was severe but numbers prevailed. Olaf's own ship, the famous Long Serpent, was boarded by Eric Hakonsson's men, and the King in the face of sure capture leaped into the Baltic.[50]
The victors had agreed to divide up Norway and the agreement was carried out. Most of the coast lands from the Naze northwards were given to Earl Eric. The southern shores, the land from the Naze eastwards, fell to King Sweyn. Seven shires in the Throndhjem country and a single shire in the extreme Southeast were assigned to the Swedish King; but only the last-mentioned shire was joined directly to Sweden; the northern regions were given as a fief to Eric's younger brother Sweyn who had married the Swede-king's daughter. Similarly Sweyn Forkbeard enfeoffed his son-in-law Eric, but the larger part he kept as his own direct possession.[51]
The battle of Swald was of great importance to the policies of the Knytlings. The rival Norse kingdom was destroyed. Once more the Danish King had almost complete control of both shores of the waterways leading into the Baltic. Danish hegemony in the North was a recognised fact. But all of Norway was not yet a Danish possession—that ambition was not realised before the reign of Canute. And England was still unconquered.
