The missionary St Ansgar met Swedish kings at Birka when he visited in 829 – 30 and 851 – 2, but there is no evidence of a royal residence on the island. Birka was probably administered from a royal estate at Hovgården on the neighbouring island of Adelsö, a couple of miles away, rather as Hedeby was administered from the royal estate at Flüsing. One of the five large burial mounds at Hovgården, known collectively as the Kungshögar (‘the kings’ barrows’), was excavated a century ago and was found to contain the remains of a high status male who had been cremated in a boat along with horses, cattle and dogs some time around 900. Birka seems to have been abandoned quite abruptly during the reign of Erik the Victorious. A complete absence of Anglo-Saxon coins suggests that this must have happened before Æthelred II began paying enormous sums in Danegeld to the Vikings in the 990s: thousands of his coins have been found in Scandinavia and some of them, at least, would have found their way to Birka had it still been occupied. There is no evidence that Birka met a violent end so it is likely that trade simply shifted to the new town, founded by Erik c. 980, of Sigtuna on the northern shore of Lake Mälaren about 15 miles south of Uppsala.
Sweden comes more fully into the light of recorded history during the reign of Erik’s son Olof Skötkonung (‘treasure king’) (r. 995 – 1022). Olof’s reign is enormously significant both because he was Sweden’s first Christian king and because he was the first king who is known to have ruled both the Swedes and the Götar, so laying the foundations of the medieval Swedish kingdom. However, those foundations were very shaky and it was well into the twelfth century before Sweden was a fully Christianised, unified kingdom. The paucity of sources for Viking Age Sweden makes it impossible to know how Olof actually came to rule over both the Swedes and the Götar. Presumably dynastic connections between the two peoples already existed and there may have been earlier kings who ruled over both areas: there is certainly no reason to assume that Olof’s achievement was unprecedented or that he came to rule the Götar by conquest rather than by election at the regional things held annually in Västergötland and Östergötland. However, Olof’s union of the two people was also not final because many of his successors did not exercise authority over the Götar. Sometimes, the Götar elected different kings to the Swedes, on other occasions they did without a king altogether and were ruled by their own chiefs and lawspeakers. The achievement of stable dynastic rule was made more difficult in Sweden because, unlike in Denmark and Norway, it was not necessary to have royal blood to be chosen as a king. The Viking Age was a distant memory when the Swedes and Götar were at last permanently united in 1173 by Knut Eriksson (r. 1167 – 96).
The fragility of the Swedish kingdom contributed to the slow acceptance of Christianity. In Denmark and Norway forceful action by kings overcame pagan opposition to Christianity, but Swedish kings had to act with greater circumspection. Pagan Swedish kings did not actively oppose missionary activity. The kings who Ansgar met at Birka gave him permission to preach after consulting the local thing, but they showed no interest in converting themselves and, without royal backing, he failed to found lasting Christian communities. The missionary effort was renewed by Unni, like Ansgar an archbishop of Hamburg-Bremen, but he died at Birka in 936 with little to show for his efforts. The conversion of the Danes under Harald Bluetooth gave missionary efforts in Sweden a new impetus. During Erik’s reign a Danish missionary, Bishop Odinkar Hvite the Elder, began the conversion of the Götar from his base at Skara in Västergötland. Adam of Bremen believed that Odinkar enjoyed so much success because, as a Dane, ‘he could easily convince the barbarians of everything about our religion’. Erik was himself baptised when he was in Denmark in the 980s or early 990s, but Adam says that he renounced Christianity as soon as he returned to Sweden. The traditional story of Olof Skötkonung’s conversion is that he was baptised by St Sigfrid, an English missionary from Glastonbury, in 1008 at Husaby, not far from Skara. This date is probably too late: Olof used Christian imagery on the coins issued at the new town of Sigtuna right from the beginning of his reign, so he may really have been baptised before he became king. It is possible that the young Olof was baptised at the same time as his father, but was more receptive to the new religion. ‘God’s Sigtuna’, as Olof called the town on his coins, seems to have had a largely Christian population right from its foundation, because few pagan burials have been discovered in its extensive cemeteries. It was probably Olof’s intention that Sigtuna would be a Christian counter-balance to the nearby pagan cult centre at Uppsala and he founded several churches there. Olof began to give Sweden a formal ecclesiastical organisation, founding a bishopric at Skara in 1014, but the strength of pagan sentiment was such that he never risked trying to convert the Swedes by force. Olof’s softly-softly approach to promoting Christianity was still too much for devout pagans and towards the end of his reign he was forced to share power with his son Jacob, who succeeded him after his death in 1022. The pagans detested Jacob’s biblical name and they forced him to adopt the proper Swedish name Önund when he became king.
Changing his name was about the limit of Önund’s compromise with the pagans. He and his immediate successors continued to co-operate with the church, encourage missionary activity, and extend the country’s diocesan structure. By around 1080, paganism was dying out among the Götar, and missionaries were travelling the countryside destroying the last temples and pagan idols. The Swedes, however, stubbornly resisted conversion. Missionary bishops believed that paganism would never collapse unless the temple at Uppsala was destroyed, but Swedish kings refused to sanction the use of force. Önund did not retaliate when an over-enthusiastic English missionary called Wilfrid was hacked to pieces by a pagan mob after he provocatively destroyed an idol of Thor at Uppsala in the 1030s. Thirty years later, king Stenkil (r. 1060 – 66) refused to allow Adalvard, the newly appointed bishop of Sigtuna, to destroy the temple at Uppsala, fearing that this would provoke a pagan uprising. He was right to be wary. Stenkil’s son Inge the Elder, who became king around 1080, was a more militant Christian, but when he tried to outlaw paganism at the thing at Uppsala, he was pelted with stones and had to flee into exile in Västergötland. In Inge’s place, the Swedes chose his brother-in-law Blót-Sven (‘sacrifice-Sven’), who agreed to reinstate paganism and perform the traditional sacrifices. Immediately, a horse was brought and cut into pieces for eating and a sacred tree was smeared with its blood. Sven reigned only for about three years. In exile, Inge raised a small mounted force and invaded Svealand, taking Sven by surprise in the early hours of the morning in his hall. After surrounding the place, Inge’s men set the hall on fire. The few who managed to get out of the burning building were butchered by Inge’s men. Sven’s death broke pagan resistance to Christianity. Restored to the throne, Inge resumed his anti-pagan crusade and soon afterwards the cult centre at Uppsala was destroyed and replaced with a church. By the time Inge died in 1105, Sweden was mainly Christian. The death of the old gods, so long prophesised, had finally come to pass.