How Did the Vikings Convert to Christianity?
The Vikings are known today for being piratical raiders of Europe, capturing whatever goods they could, including people, in lighting raids and then returning to their homes in Scandinavia. Churches and monasteries were among their favorite targets because the structures were usually not very well protected yet they often held great amounts of gold and other treasures. To the early Vikings, these churches represented nothing more than potentially lucrative targets – the religious connotation meant little to them one way or another. The Vikings followed an Indo-European religion that many of the people of Europe practiced before they became Christians. The Vikings believed that gods and goddesses such as Odin, Thor, Freya, and Tyr watched over them as they went into battle and traversed the seas in their long ships. But by the late eleventh century the old gods were becoming a thing of the past and the Vikings were embracing Jesus.
The Vikings were among some of the last Europeans to embrace Christianity and the manner in which they did so, and the reasons for their conversion, were complex. Europeans began sending missionaries to the north in the ninth century and gradually the various Viking kingdoms began to convert. Most of the early Viking rulers converted due to political and economic ties with Christian Europe and then forced their subjects to follow suite. The conversion process was uneven across Scandinavia and there were heathen/pagan reactions to Christianity, but by early twelfth century the process was complete and Scandinavia was integrated into greater Western Civilization.
Denmark and the First Christian Missions
Due to its close proximity to the Holy Roman Empire and the rest of Europe, Denmark was the first of the Viking lands to accept Christianity. The Christianization of Denmark began when missionaries, such as Ansgar, began visiting the land in the early ninth century. Ansgar was a German monk who would later become the archbishop of Bremen.  An eleventh century monk named Adam of Bremen wrote in his History of Archbishops of Hamburg-Bremen that the pope gave the archbishopric of Hamburg-Bremen ecclesiastical authority in Scandinavia in the mid-ninth century.  The missionary efforts moved slowly until they achieved official status from a Viking king in 965.
According to the Old Norse language history of the Viking Age known as the Heimskringla, Harald Bluetooth (ruled c. 958-986) was the first Christian king of Denmark. Harald had become embroiled in a conflict with Otto II, emperor of the Holy Roman Empire (reigned 973-983), which was at least partially due to the fact that Harald was a pagan. Otto threatened to invade Denmark with an army of Germans, Franks, and Poles, forcing the Danish king to consider his options.  According to the saga, Harald was converted to Christianity after witnessing one of Otto’s priests perform an apparent miracle.
“The Emperor Otta and the Danish king met in Morsö. Then a holy bishop, Poppa, made known the true faith to King Harald; the bishop bore glowing iron in his hand and showed King Harald his and unburned. After that, King Harald let himself and all the Danish army be baptized.” 
Harald then made it his mission to convert the rest of his kingdom as well as all of his pagan cousins to the north. He is credited with converting Hakon the Jarl of Norway, but when Hakon went back to his pagan ways the two rulers went to war. 
The sagas depict the conversion of Scandinavia taking place from a “top down” perspective, where the kings and jarls converted first, often for political reasons as Harald did, and then obliging their subordinates to follow suite. A closer examination of the accounts reveals that the conversions usually followed a three step pattern: first the convert would renounce the old ways, then the convert would publicly identify as a Christian, and finally the convert would follow the rituals and inwardly adopt the new faith.  The first two steps were often superficial and done in name only – new converts to Christianity often did so under the threat of death or to gain a new ally.
King Olav Tryggvason’s Saga
After the Kingdom of Denmark converted to Christianity, missionaries made attempts in Norway that were not always so fruitful. The situation changed when Olav Tryggvason (ruled 995-1000 BC) became king, but according to the sagas, long before he ruled Norway he embarked on a journey where he gradually converted to Christianity. Norway itself was more resistant to Christianity, with the sagas noting that it was home to many “backsliders.”
“But in Norway those who had taken up Christianity fell back to the blood offering just as they had also done before in the north of the land.” 
From the age of nine to eighteen, Olav lived with his stepfather, Vladimir I (reigned 980-1015), the Grand Prince of Kiev. Vladimir was a pagan and a member of the Viking descended Rus’ culture, but he was quite tolerant toward other religious faiths, including Christianity. When Olav became an adult, he left Russia with the blessing of Harald and raided in Poland and fought alongside Harald Bluetooth, before embarking on a series of raids in the British Isles. Olav was officially baptized as a Christian while in England, but he remained a true Viking in most ways: he never preached morality to his people and he remained a quintessential warlord.  Although Olav may never have moralized to unbelievers, he was very serious about his new religion and was more than willing to use his power and influence to convert his people.
The sagas depict how Harald returned to Norway and eventually won his birthright as king. The more important subtext, though, is how he forced Christianity on the Vikings. Olav would travel throughout the country calling things, assemblies of the bonders or freemen, and give them a simple ultimatum – convert to Christianity or die.
“And since the king had there a very great strength of men, they were afraid of this; and at last the king gave them two choices, either that they should take up Christianity and let themselves by baptised, or otherwise they should hold battle with him.” 
Olav directed his conversion energies not just at his subjects, but also at the monuments and temples dedicated to the old gods. Although pagan Scandinavian “temples” were often little more than gathering places in forests, Olav did his best to erase their memory from the minds of his fellow Vikings.
“King Olav went with his army to North Möre and baptised that folk. After this he sailed into Lade and had the temple broken down and took all the goods and ornaments form the temple and from god. And from the temple door he took a great gold ring which Hacon the Jarl had caused to be made: then King Olav had the temple burned down.” Sturlason, The History of Olav Trygvason, LVIII</ref>
It should be noted that although the sagas are considered primary sources, Sturlason compiled them in the thirteenth century, more than 200 years after the events. Elements of the sagas may say just as much about the political situation in thirteenth century Iceland, Sturlason’s home country, as they do about Norway’s conversion to Christianity. With that said, the outline and basic facts of Olav’s campaign to promote Christianity in Norway are accepted by all historians. It was during the reign of his successor, Olaf Haraldsson (1015-1028), though, when the Christianization of Norway was complete. Olaf was baptized in the cathedral in Rouen, Normandy while he was away from Norway, but when he returned to reclaim his throne he did so with a particular animosity toward the pagans. He destroyed the pagan sanctuaries and made Christianity compulsory at the Moster thing in 1024. For his efforts, Olaf was later venerated as Saint Olaf by the Catholic Church. 
Christianity in Iceland, Greenland, and Sweden
Iceland was settled by explorers from Norway in the ninth century and although it was from that point forward part of Scandinavia, it was always unique in the northern lands. Iceland never had a king and its geographic distance meant that it was not introduced to Christianity until later. Once Iceland was introduced to the new religion, though, the people of the island quickly converted. The people of Iceland converted to Christianity in 1000, which was largely through the efforts of Olav Tryggvason.  The sagas offer an interesting anecdote that describes how Olav convinced one prominent Icelander to convert only after he promised him the material reward of his “friendship.”
“Kjartan was the biggest and finest of men and able of speech. And when the king and he had spoken a few words together, the king bade Kjartan take up Christianity. Kjartan said he would not say ‘nay’ to that if he should have the king’s friendship. The king promised him his full friendship and the matter was now agree upon between them.” 
After the people of Iceland had been introduced to Christianity, the Church sent members of the hierarchy to make it official. The Icelandic Bishop Isleifir was consecrated by Archbiship Adalbert in 1056, which gave Iceland’s Christians formal leadership and a connection to the Church. 
Tryggvason is also credited with spreading Christianity to the Viking colonies of Greenland. Although Tryggvason never visited Greenland, according to the sagas he played a major role in the conversion of Leif Erikson (970-1020). After meeting with Olav in Norway, Erikson returned to the Greenland colonies promoting the new religion to his followers.
Among the mainland Viking lands, Sweden was the last to accept Christianity. The first Christian king of Sweden is generally believed to be Olof Skötkonung (ruled 995-1022), although he was far less forceful in his promotion of the new religion than his Norwegian counterparts.  The legends also state that Olof was the first king of a unified Sweden and that under his rule the influence of the Church grew rapidly across the land. 
The Church established a Scandinavian archbishopric in 1104 in the city of Lund, which is now part of Sweden but was at the time in the Kingdom of Denmark.  Although elements of the Vikings’ pre-Christian culture would continue to be employed in Scandinavian art and literature for some time after 1104, the early twelfth century marked the end of the Viking pagan era and the beginning of Scandinavia’s integration into greater Western Civilization.
The process by which the Vikings adopted Christianity and integrated themselves into Western Civilization was long and somewhat complex. It began with primarily German priests and missionaries visiting Denmark and then picked up momentum when Viking kings converted to the new faith. The kings, as well as other nobles and influential men in Viking society, usually converted for reasons of status, but then later forced their subjects to also convert. The process spread throughout Scandinavia, with Christianity ultimately proving to be the only thing that could conquer the seemingly unconquerable Vikings.
- Rosedahl, Else. The Vikings. Translated by Susan M. Margeson and Kirsten Williams. (London: Penguin, 1998), p. 159
- Sawyer, Birgit. “Scandinavian Conversion Histories.” Harvard Ukrainian Studies 12/13 (1989) p. 47
- Sturlason, Snorre Heimskringla: Or the Lives of the Norse Kings. (Mineola, New York: Dover, 1990), The History of Olav Trygvason, XXVIII
- Sturlason, The History of Olav Trygvason, XXVIII
- Sturlason, The History of Olav Trygvason, XXXIII
- Abram, Christopher. “Modeling Religious Experience in Old Norse Conversion Narratives: The Case of Óláfr Tryggvason and Hallfreðr vandræðskáld.” Speculum 90 (2015) p. 119
- Sturlason, The History of Olav Trygvason, LIII
- Abram, p. 124
- Sturlason, The History of Olav Trygvason, LVIII
- Rosedahl, pgs. 165-6
- Rosedahl, p. 165
- Sturlason, The History of Olav Trygvason, LXXXII
- Sawyer, p. 47
- Sturlason, The History of Olav Trygvason, LXXXVI
- Rosedahl, p. 166
- Sawyer, p. 55
- Sawyer, p. 49