The place cannot now be identified, as the formation of the Baltic coast has been much modified in the course of subsequent centuries, partly by the gradual silting up of the sea, and partly by the storms of the 14th century. Swold was an island probably on the North German coast, near Rügen. The battle was fought between Olaf Trygvesson, king of Norway, and a coalition of his enemies: Eric Hakonson, his cousin and rival; Olaf, the king of Sweden; and Sweyn Forkbeard, king of Denmark. The poets, and the poetically minded authors of the sagas, who are the only authorities, have told the story with many circumstances of romance. But when the picturesque details, which also have no doubt at least a foundation of truth, are taken at their true value, the account of the battle still presents a very trustworthy picture of the sea-fighting of the Norsemen.
Olaf had been during the summer in the eastern Baltic. The allies lay in wait for him at the island of Swold on his way home. The Norse king had with him seventy-one vessels, but part of them belonged to an associate, Sigwald, a chief of the Jomsburg vikings, who was an agent of his enemies, and who deserted him. Olaf's own ships went past the anchorage of Eric Hakonson and his allies in a long column without order, as no attack was expected. The king was in the rear of the whole of his best vessels. The allies allowed the bulk of the Norse ships to pass, and then stood out to attack Olaf. He might have run past them by the use of sail and oar to escape, but with the true spirit of a Norse warrior he refused to flee, and turned to give battle with the eleven ships immediately about him. The disposition adopted was one which is found recurring in many sea-fights of the middle ages where a fleet had to fight on the defensive. Olaf lashed his ships side to side, his own, the Long Serpent, the finest war-vessel as yet built in the north, being in the middle of the line, where her bows projected beyond the others. The advantage of this arrangement was that it left all hands free to fight, a barrier could be formed with the oars and yards, and the enemy's chance of making use of his superior numbers to attack on both sides would be, as far as possible, limited - a great point when all fighting was with the sword, or with such feeble missile weapons as bows and javelins. The Norse long ships were high in the bulwark - or, as the Greeks would have said, cataphract. Olaf, in fact, turned his eleven ships into a floating fort.
The Norse writers, who are the only authorities, gave all the credit to their own countrymen, and according to them all the intelligence of Olaf's enemies, and most of their valour, were to be found in Eric Hakonson. They say that the Danes and Swedes rushed at the front of Olaf's line without success. Eric Hakonson attacked the flank. His vessel, the Iron Ram, was "bearded," that is to say, strengthened across the bows by bands of iron, and he forced her between the last and last but one of Olaf's line. In this way the Norse ships were carried one by one, till the Long Serpent alone was left. At last she too was overpowered. Olaf leapt into the sea holding his shield edgeways, so that he sank at once and the weight of his hauberk dragged him down. A legend of later days has it that at the last moment a sudden blaze of light surrounded the king, and when it cleared away he had disappeared. King Olaf is one of the same company as Charlemagne, King Arthur and Sebastian of Portugal - the legendary heroic figures in whose death the people would not believe, and whose return was looked for.