Thorfinn and Rognvald had fallen out in time.

The vivid account of the war between Thorfinn and Rognvald in the Orkneyinga Saga which survives may well be only a part of a much longer saga now lost.

Their enmity arose with the arrival of Kalf Arnesson and his followers in Orkney.

Kalf is the uncle of Thorfinn's wife Ingibiorg Finnsdottir, and had left Norway to escape King Magnus Olafsson.

Rognvald, with Kalf's brothers, had shared Magnus's exile in Kievan Rus under the protection of Prince Yaroslav the Wise, and the saga says that when Kalf came to Ladoga to invite Magnus back to Norway, Rognvald almost attacked him.

Thorfinn, it is said, found hosting Kalf and his men a burden, and in time asked Rognvald to return the third of the earldom "which had once belonged to Einar Wry-Mouth".

Rognvald refused, saying that it was for King Magnus to settle matters.

Thorfinn began raising an army, and Rognvald's islanders were unwilling to fight Thorfinn, so Rognvald sailed to Norway where King Magnus supplied him with ships and men.

He returned to the islands, facing Thorfinn and Kalf Arnesson in a sea battle which Arnor the skald commemorated in verse.

The battle went Rognvald's way to begin with, but in the end he was defeated and forced again to seek refuge with King Magnus.

King Magnus offers to fit out another expedition for Rognvald, but he decides to take just one ship and a picked crew.

He sails to Shetland in winter, and learning that Thorfinn is staying on a farm on the Orkney Mainland with only a few men, he sets out at once to attack him.

Rognvald's men surprise Thorfinn, and set the farm ablaze.

The saga says that Thorfinn had to break down a wall and escape, carrying his wife in his arms, flying south to Caithness for safety.