The later Norse sagas relate that a brief but serious conflict flared up with the Norwegian king
Harald Hardrada in 1064–65. One of Harald's foremost men
Håkon Jarl, was married to the king's niece Ragnhild and followed Harald on his military expeditions against the Danish ruler
Sweyn Estridsen. According to
Snorri Sturluson's
Heimskringla the Norwegians were victorious at the
Battle of Nissan in 1062, but Håkon Jarl secretly allowed the defeated Sweyn to escape alive. When this was later reported to Harald Hardrada, the enraged king gave orders to kill Håkon, who however managed to escape to Sweden. The escapee stayed with King Stenkil who made him Jarl of
Värmland. According to another saga,
Morkinskinna, Håkon Jarl left Norway for
Denmark where he was created Jarl of
Halland. Meanwhile, Harald Hardrada concluded peace with Sweyn Estridsen in 1064 and then started to harry in Stenkil's realm in
Götaland. The worried Stenkil arranged a meeting with King Sweyn and asked for his support. Sweyn replied that he could not break the recent peace treaty, but advised Stenkil to appoint the valiant Håkon Jarl as sub-ruler of Västergötland, from where he could confront King Harald. This was arranged, and Håkon assembled men from Denmark as well as from the two Geatic provinces. He spoke to his troops at an assembly, where he self-assuredly said: "Even though I have a lesser title than King Stenkil, it may be that I will be of no less assistance, for he is used to an easy life, while I am accostumed to battles and hard conditions". According to all the saga versions, Harald Hardrada reacted to Håkon Jarl's Swedish position by assembling a fleet and invading Stenkil's kingdom in the cold of the winter. At the entrance of the
Göta älv, he took the lighter boats and brought them upriver, to Lake
Vänern. The ships then rowed eastwards, to the place where he heard that Håkon's troops had assembled. With Håkon was the law-speaker (
lagman) of the Geats, Thorvid. However, the Geats were lightly clothed, "as is always the case with the Geats", while Harald's troops were more numerous and better equipped. The Geatic law-speaker lost his head and took to his heels before the battle had begun. In the fight that followed, Håkon's troops were defeated with losses. Nevertheless, Harald did not push his advantage further, but returned to the lake shore with his men. The end of the expedition was inauspicious. Part of Harald's troops were led into a trap, ambushed and massacred by Håkon's men. As the Norwegians sailed down the Göta älv, some more were killed by Geatic archers. In the following year 1066 Harald Hardrada undertook his
ill-fated invasion of
England, which left the striking power of the Norwegian kingdom crippled. Håkon Jarl ended his life as a magnate in Denmark. It is not clear how much of the internally differing saga accounts can be regarded trustable, but a preserved scaldic verse by
þjóðólfr Arnórsson confirms the outlines: ::Stenkil's men who would ::give support to the Jarl ::have been assigned to death ::the ruler caused this. ::Håkon withdrew ::quickly when support failed. ::Thus says the one who wants ::to depict this nicely.
Morkinskinna indicates that the relations between Stenkil and Sweyn Estridsen were amicable. It is likely that the Swedish ruler had an interest in supporting Sweyn against the attempts of Harald Hardrada to subjugate Denmark between 1047 and 1062. Historian Aksel E. Christensen has concluded that the Norwegian-Danish peace treaty of 1064 was a success for the Swedish policy to prevent one king from ruling the kingdoms to the north and the south of
Skagerrak. Strangely, the
Knytlinga Saga tells that "King Sweyn also had a dispute with the Swedish King Stenkil, who went with his army against King Sweyn, although he did not appropriate any of his territories". ==Death and burial==