The Chronicle of The Kings of Norway
Part 109 - Earl Sigvalde's Treacherous Plans
At the same time that king Svein sent a message to Svithjod for an army, he sent Earl Sigvalde to Vindland to spy out King Olaf Trygvason's proceedings, and to bring it about by cunning devices that King Svein and King Olaf should fall in with each other. So Sigvalde sets out to go to Vindland. First, he came to Jomsborg, and then he sought out King Olaf Trygvason.
There was much friendship in their conversation, and the earl got himself into great favour with the king. Astrid, the Earl's wife, King Burizleif's daughter, was a great friend of King Olaf Trygvason, particularly on account of the connection which had been between them when Olaf was married to her sister Geira.
Earl Sigvalde was a prudent, ready-minded man; and as he had got a voice in King Olaf's council, he put him off much from sailing homewards, finding various reasons for delay. Olaf's people were in the highest degree dissatisfied with this; for the men were anxious to get home, and they lay ready to sail, waiting only for a wind.
At last Earl Sigvalde got a secret message from Denmark that the Swedish king's army was arrived from the east, and that Earl Eirik's also was ready; and that all these chiefs had resolved to sail eastwards to Vindland, and wait for King Olaf at an island which is called Svold. They also desired the earl to contrive matters so that they should meet King Olaf there.