A few years later there appeared at the Danish court a young, handsome, talented chief, the famous Earl Hakon whose father, Sigurd, earl in the Throndelaw, the sons of Eric had treacherously slain. The King of Denmark had finally discovered that his foster-son was anything but an obedient vassal, and doubtless rejoiced in an opportunity to interfere in Norwegian affairs. Harold Grayfell was lured down into Jutland and slain. With a large fleet the Danish King then proceeded to Norway. The whole country submitted: the southern shores from the Naze eastward were added to the Danish crown; the Throndelaw and the regions to the north were apparently granted to Earl Hakon in full sovereignty; the rest was created into an earldom which he was to govern as vassal of the King of Denmark.[13]
A decade passed without serious difficulties between vassal and overlord, when events on the German border brought demands on the earl's fidelity to which the proud Norseman would not submit. It seems probable that King Harold in a vague way had recognised the overlordship of the Emperor; at any rate, in 973, when the great Otto was celebrating his last Easter at Quedlingburg, the Danish King sent embassies and gifts.[14] A few weeks later the Emperor died and almost immediately war broke out between Danes and Saxons.
Hostilities soon ceased, but the terms of peace are said to have included a promise on Harold's part to introduce the Christian faith among his Norwegian subjects. Earl Hakon had come to assist his overlord; he was known to be a zealous heathen; but King Harold seized him and forced him to receive baptism. The earl felt the humiliation keenly and as soon as he had left Denmark he repudiated the Danish connection and for a number of years ruled in Norway as an independent sovereign.[15] King Harold made an attempt to restore his power but with small success. However, the claim to Norway was not surrendered; it was successfully revived by Harold's son Sweyn and later still by his grandson Canute.
Earl Hakon's revolt probably dates from 974 or 975; King Harold's raid along the Norse coasts must have followed within the next few years. The succeeding decade is memorable for two notable expeditions, the one directed against King Eric of Sweden, the second against Hakon of Norway. In neither of these ventures was Harold directly interested; both were undertaken by the vikings of Jom, though probably with the Danish King's approval and support. The Jomvikings were in the service of Denmark and the defeat that they suffered in both instances had important results for future history. The exact dates cannot be determined; but the battles must have been fought during the period 980-986.
In those days the command at Jomburg was held by Styrbjörn, a nephew of the Swedish King. Harold Bluetooth is said to have given him the earl's title and his daughter Thyra to wife; but this did not satisfy the ambitious prince, whose desire was to succeed his uncle in Sweden. Having induced his father-in-law to permit an expedition, he sailed to Uppland with a strong force. The battle was joined on the banks of the Fyris River where King Eric won a complete victory. From that day he was known as Eric the Victorious.[16]
Styrbjörn fell in the battle and Sigvaldi, the son of a Scanian earl, succeeded to the command at Jomburg. In some way he was induced to attack the Norwegian earl. Late in the year the fleet from the Oder stole northwards along the Norse coast hoping to catch the earl unawares. But Hakon's son Eric had learned what the vikings were planning and a strong fleet carefully hid in Hjörunga Bay lay ready to welcome the invader.
The encounter at Hjörunga Bay is one of the most famous battles in Old Norse history. During the fight, says the saga, Earl Hakon landed and sacrificed his young son Erling to the gods. The divine powers promptly responded: a terrific hailstorm that struck the Danes in their faces helped to turn the tide of battle, and soon Sigvaldi was in swift flight southwards.[17]
As to the date of the battle we have no certain knowledge; but Munch places it, for apparently good reasons, in 986. Saxo is probably correct in surmising that the expedition was inspired by King Harold.[18] As to the significance of the two defeats of the Jomvikings, there can be but one opinion: northward expansion of Danish power had received a decisive check; Danish ambition must find other fields.