Olaf spent the winter in the Uplands, and in the spring gathered an army with which he intended to meet Earl Svein. The kings in Hedemarken furnished him with many armed men, and his stepfather, Sigurd Syr, joined him with a great force. During the winter he had built a ship, which was named “Karlshoved” (Carl’s Head, possibly intended to represent the head of Charlemagne, whose name was held in great veneration). On the bow of the ship was a crowned head, which the king himself had carved. With a fine and well-equipped fleet Olaf set out from Viken, going first to Tunsberg.
Earl Svein in the meanwhile collected a great force in the north. Many of the chiefs were his relatives and friends, and were able to give him great assistance. His brother-in-law, Einar Thambaskelfer, was on his side, and with him many other lendermen (a sort of local governors); and among them were many who had taken oath of allegiance to King Olaf the winter before. Earl Svein sailed south along the coast, drawing men from every district. When they came to Rogaland, Erling Skialgson of Sole joined them with a considerable force. Svein’s fleet is said to have consisted of forty-five ships, with probably upward of 2,500 men; Olaf hardly had half the number of ships, but his ships were considerably larger, so that the number of men was probably about the same. Toward the end of Easter he entered Viken with his fleet and put in at Nesiar (Nesje), a headland on the east side of the bay (near Fredriksværn).
On Palm Sunday, March 25, 1016, the two fleets met in battle. Before opening the battle Olaf had his ships tied together, his own ship, “Karlshoved,” occupying a place in the centre. On this ship were one hundred and twenty men armed in coats of mail, French helmets, and white shields, on which was a gilt or painted cross. Olaf had a white banner on which the figure of a serpent was sewed. The king instructed his men to defend themselves with the shields in the beginning, and take care of their lances and arrows, so that they were not thrown away to no purpose. This advice was followed with good results. When the conflict had become exceedingly sharp, and the missiles began to be scarce on the earl’s side, Olaf’s men were well supplied, and their attack was very severe. Men fell in great numbers on both sides, but mostly on the earl’s ships. King Olaf with the “Karlshoved” engaged Earl Svein’s ship, and his men were soon preparing to enter it. The earl, seeing his defeat, ordered his ship cut loose from the others, and at the last moment his brother-in-law, Einar Thambaskelfer, succeeded in pulling the ship out of the line of battle from behind, using his own vessel as a tow-boat. When the earl’s ship was gone, the flight became general. Some of the earl’s men fled up the country, others surrendered on the king’s mercy, but Earl Svein and his followers escaped out through the bay. Svein proceeded to Sweden to seek the aid of the Swedish king, while Erling Skialgson and some other chiefs sailed westward and returned to their homes. Earl Svein was well received by King Olaf the Swede, and it was agreed that next winter they should proceed with an armed force overland through Helsingland and Jemteland and down to the Throndhjem country, for the earl depended upon the faithful help of the people there. The summer was to be spent in viking expeditions in the Baltic. Svein made a cruise to Russia and plundered the coasts; in the fall he was taken sick there and died (1016).
King Olaf went north after the battle of Nesje, and settled down in Nidaros, where he rebuilt the royal residence and the church, and helped the merchants to rebuild the town. After the death of Earl Svein he was readily recognized by all the people in that part of the country as the rightful king. The Swedish king became very angry when he heard that he had lost the possessions in Norway which he had won by the battle of Svolder, and he threatened to take great revenge upon Olaf the Big, a nickname which he had given his Norwegian opponent on account of his stoutness. He sent tax-collectors into Norway, and when these were harshly treated, some of them even being killed, Olaf the Swede was highly enraged, and war between the two kings was threatened. King Olaf made preparations for an emergency, although he much preferred peace, and even wished to marry the Swedish king’s daughter. He built fortifications on a headland in the river Glommen, near the falls of Sarpen, and around these fortifications he laid the foundation of the town of Borg or Sarpsborg. The people on both sides of the boundary were very much displeased with the feud between the kings, and on both sides the kings were urged to make peace. The Norwegian king was willing enough, and sent conciliatory messages to Olaf the Swede, but the latter rejected all overtures. Finally the matter was brought to a crisis at a general Thing assembled at the Swedish city of Upsala. Here the king at first also refused to hear the propositions for peace, when Thorgny Lagman (lawman, a kind of judge at the Thing) rose, and made the following speech: “The disposition of Swedish kings is different now from what I hear it was formerly. My grandfather, Thorgny, could well remember the Upsala king Erik Eymundson, and used to tell of him that when he was in his best years he went out every summer on expeditions, and conquered Finland and Karelen, Esthonia and Courland and many parts of the eastern country. Even at the present day the earth-bulwarks and other great works which he made are to be seen. And yet, he was not so proud that he would not listen to those who had something to say to him. Thorgny, my father, was a long time with King Biorn, and well knew his ways and manners. At that time the kingdom was in great power and suffered no losses. He, too, was sociable with his men. I also remember Erik the Victorious, and was with him on many a war expedition. He enlarged the Swedish dominion and bravely defended it, and with him also it was easy to talk about public affairs. But the king we now have allows no one to talk with him of anything but what he himself desires to hear. He wants to have Norway laid under him, which no Swedish king before him ever desired, and thereby causes many men to be alarmed. But now it is the will expressed by us peasants that thou, King Olaf, make peace with the king of Norway, and give him thy daughter Ingegerd in marriage. If thou wilt reconquer the countries on the Baltic which thy relations and ancestors had there, we will all go with thee. But if thou wilt not now consent to what we demand, we will no longer suffer law and peace to be disturbed, but will attack thee and kill thee. So our forefathers did when, at the Mora Thing, they drowned five kings in a morass because they were filled with the same insupportable pride thou hast shown toward us. Now tell us, in all haste, which of these two conditions thou wilt choose.” The whole public approved, with clash of arms and shouts, the speech of Thorgny Lagman. Then the king rose and said he would do as the people desired. “All Swedish kings,” he said, “have done so, and have allowed the peasants to rule in all according to their will.” The murmur among the people then came to an end, and it was decided that the terms of peace offered by the Norwegian king were to be accepted, and that Ingegerd, the king’s daughter, was to be married to King Olaf of Norway.
In the meanwhile King Olaf travelled through the country, and carefully investigated the manner in which Christianity was observed. Where he found the people lacking in Christian knowledge, he taught them and furnished them with Christian teachers. If he met with obstinate opposition, he acted with severity and cruelty. “If any there were,” says the saga, “who would not renounce heathen ways, he took the matter so zealously that he drove some out of the country, mutilated others on hands or feet, or stung their eyes out; hanged some, slew some with the sword; but let none go unpunished who would not serve God.” In this way he proceeded through the country, accompanied by three hundred and sixty armed men.
King Olaf soon found that Christianity was thriving less the further he proceeded into the interior. In the Uplands five small kings came together at Ringsaker, and under the leadership of King Rorek conspired to kill King Olaf. “But it happened here,” says the saga, “as it usually does, that every one has some friend even among his enemies.” Ketil Kalf of Ringenes, who was present at the meeting of the conspirators, went down after supper to the lake (Miösen), and boarded a little vessel which King Olaf had made him a present of after the battle at Nesje. He had forty well-armed men with him, and rowed in all haste down the lake. He arrived early in the morning at Eid (Eidsvold), where he found the king and told him of the intention of the small kings of Upland. King Olaf immediately gathered his men, sailed north to Ringsaker, surprised the conspirators, and captured them.
King Olaf now availed himself of the opportunity that chance had given him, to rid himself of royal rivals who, as descendants of Harald the Fairhaired, claimed under the law to have as much right to their possessions as any supreme king, and who had always been in the way of a national unity. King Olaf now, by one decisive act, secured the unity and independence of the country, and prepared the way for the victorious entrance of Christianity.
King Ring and two other kings were banished from Norway, under oath never to return. Rorek was a treacherous man and could not be depended upon, so the king ordered both his eyes put out, and afterward took him with him in that condition wherever he went. He ordered Gudrod Valley-king’s tongue to be cut out, and of the lendermen and peasants who were implicated in the conspiracy some he banished from the country, some he mutilated, and with others he made peace. King Olaf took possession of the land that these kings had possessed. His stepfather, Sigurd Syr, who had had nothing to do with the conspiracy of the other small kings, died during the winter (1018), and now Olaf alone bore the title of King in Norway.
Shortly after his stepfather Sigurd Syr’s death, Olaf went to visit his mother, Aasta, and on this occasion it is told that she took her boys (half-brothers of Olaf) to show them to the king. King Olaf took Guthorm on one knee and his brother Halfdan on the other. He made a wry face at the boys, and pretended to be angry, and they became frightened and ran away. Then Aasta brought in her youngest son, Harald, who was then three years old. The king made a wry face at him also, but the boy only stared back at him. The king then took hold of the boy’s hair as if to pull it, but the boy in return pulled the king’s whiskers. “Thou wilt probably be revengeful some day, my friend,” said the king. The following day Olaf and Aasta were watching the boys at play down by the lake (at the Tyrifjord). Guthorm and Halfdan had built houses and barns and had little figures representing cattle and sheep. Little Harald was down by the water, where he had little chips of wood floating. The king asked him what they were, and Harald answered that they were warships. The king laughed, and said: “The time may come, kinsman, when thou wilt command ships.” Then the king called Guthorm and Halfdan up to him, and asked them what they would like to have above all. “Fields,” answered Guthorm. “And how large?” asked the king. “I would have that headland yonder sown with corn every summer,” answered the boy. The headland included ten farms. “There would be a great deal of corn there,” said the king. Turning to Halfdan, he asked what he would like best to have. “Cows,” said Halfdan. “And how many?” asked the king. “So many that when they came to the lake to drink they would stand close together around the whole lake,” was the answer. “You both take after your father in wanting a great husbandry,” said the king. “But what wouldst thou have?” he asked Harald. “Men,” replied the boy. “And how many?” “So many that in a single meal they would eat all of Halfdan’s cows,” was the answer. The king laughed, and said to Aasta: “Here, mother, thou art bringing up a king.” “And more is not related of them on this occasion,” says the saga; but the prophecy was fulfilled, for Harald, Sigurd’s son, in time became king of Norway.
The Swedish king broke the promises he had given at the Upsala Thing, and did not send his daughter Ingegerd to the appointed meeting-place on the boundary, when King Olaf of Norway came to fetch his bride. Shortly afterward the Swedes revolted, and the Swedish king again had to make concessions, and promise to make peace with the king of Norway. The latter had, in the meanwhile, against the wishes of her father, married Astrid, a younger half-sister of Ingegerd. At the peace of Konungahella, where the kings finally met, this marriage was approved by the Swedish king, the boundary lines between the two countries were finally agreed upon, and friendly relations were established.