For the Christian missionaries who traveled the North, performance of miracles was a great publicity tool. Medieval German chronicler Adam of Bremen records the great success in Denmark of a missionary named Poppo. In order to impress the local pagans with a sign of God's power, he held a red-hot iron in his hand with no apparent damage to himself. He followed up this “miracle” by putting on a waxed tunic, standing in the middle of the crowd, and directing “that it be set on fire in the name of the Lord.” The garment burned up into ashes, and the smiling missionary attributed his safety to the power of Heaven. Because of these two acts, according to Adam of Bremen, “many thousands then believed through him.”
Others were enticed into the new faith through personal gain of wealth and power. In 911, King Charles the Simple purchased peace in his Frankish kingdom by giving the Norse outlaw Gangr Hrolf (“Hrolf the Walker”) the dukedom of all of Neustria that was held by his Viking warriors. The two conditions of the treaty were that Hrolf would defend his new lands against other northern invaders and that he would convert to Christianity. Hrolf accepted the terms, and in 912 he became a duke to Charles and underwent the rite of baptism, as did a great number of his followers. Many of them were so enthusiastic that they were baptized up to twenty times. Converts were given white garments at the ceremony, and the Vikings filled their clothing chests with the new outfits; the motive for repeated baptism was less spiritual than it was material (literally).
Hrolf himself lived a dual religious life. At his funeral, he provided large donations for masses to be sung at various monasteries, but he also ordered the sacrifice of 100 prisoners. This was echoed, on a smaller and less violent scale, in the 7th century church belonging to King Redwald of East Anglia. It had a large altar for sacrifices to Christ and a smaller one for the pagan gods. The new converts, it seemed, liked to hedge their bets.
Many Norse converts viewed Christ as a powerful new god to be placed side-by-side with the old gods. In Iceland, Helgi the Lean “believed in Christ, and yet made vows to Thor for sea-voyages and in tight corners, and for everything which struck him as of real importance.” Sea journeys seemed particularly dangerous for priests, who were considered to bring bad sailing luck. At the first sign of bad weather, the Viking sailors unhesitatingly dumped them overboard. Maybe the Viking raiders on Lindisfarne in 793 drove priests into the sea to insure good weather for their voyage home.
When all else failed, conversion to Christianity was brought about through force or the threat of violence. On the Eller River at Werden in 782, the Frankish Emperor Charlemagne beheaded 4,500 captured Saxons who would not convert to Christianity. Within three years, the leaders of the Saxon rebellion voluntarily underwent baptism. Whether Charlemagne’s motives were truly religious or merely political is difficult to say, but the mass beheadings followed close on the heels of the slaughter of a vast number of the emperor’s troops by Saxon forces.
In Kiev, Vladimir came to power in 980 AD and decided to convert his largely Norse population to a monotheistic faith for political reasons. He sent envoys to foreign lands to gather information about Judaism, Islam, Catholicism, and the Orthodox Church. He picked the Orthodox faith and had his soldiers pull down the statue of Thor, beat it, and throw it in the Dnieper River. He then forced the entire population into the water for a mass baptism. Saint Columban attempted the same sort of idol-drowning, but was driven out by the German tribe of the Alemanni for throwing statues of three of their gods into lake the lake known as the Bodensee (“Odin's lake”).