The Vikings were arguably the most destructive force in early medieval Europe. Libraries burned. Rare works of art looted and lost forever. Towns and villages wiped off the landscape. Lives destroyed. And the future of England, Ireland, and France—the primary targets of the Norsemen—placed in severe jeopardy. And this month of June marks the 1224th anniversary of when the apocalypse began.

In his entry for June 793, the anonymous monk who kept The Anglo-Saxon Chronicle, a year-by-year record of memorable events of his day, wrote, “The pagans from the northern regions came with a naval force to Britain like stinging hornets and spread on all sides like fearful wolves, robbed, tore and slaughtered… priests and deacons, and companies of monks and nuns. And they came to the church of Lindisfarne, laid everything waste with grievous plundering, trampled the holy places with polluted steps, dug up the altars and seized all the treasures of the holy church. They killed some of the brothers, took some away with them in fetters, many they drove out, naked and loaded with insults, some they drowned in the sea."

Lindisfarne Island is not much to look at—about three miles of scrubby landscape off the coast of northern England, approximately 9 miles south of the Scottish border. Yet for the English this was a place of great sanctity, the cradle of many saints, most famously St. Cuthbert, one of the most beloved figures in the history of the Church in England.

In life Cuthbert had been as renowned for his personal charm as for his personal holiness. He possessed a gentle, persuasive manner that could reconcile the bitterest enemies and bring even hardened sinners back to God. Cuthbert spent 23 years at Lindisfarne, first as prior and then as bishop.

After his death, a host of miracles were attributed to his intercession, which ensured St. Cuthbert’s continuing popularity and made his tomb in Lindisfarne’s monastery church a goal for pilgrims. Consequently, the slaughter of Cuthbert’s monks and the ruination of his shrine shocked the English. Writing from the court of Charlemagne where he ran the emperor’s palace school, the English monk Alcuin asked the Bishop of Lindisfarne (who somehow survived the raid), “What assurance is there for the churches of Britain if St. Cuthbert, with so great a number of saints, defends not his own?”

Alcuin had a point. But if Lindisfarne was exceptionally holy, it was also exceptionally wealthy.

The eighth century was a period of profound religious devotion, when the life of a monk or a nun was held in high esteem by all classes of English society. Godliness, combined with new wealth and a flowering of the arts, expressed itself in lavish gifts to churches, monasteries, and convents. Gospel books received golden covers. Shrines of the saints were plated with silver and studded with precious stones. Bishops entered their cathedrals holding crosiers of intricately carved ivory. For the Christians of England these sumptuous displays demonstrated their love for God, His saints, and the Church; it never occurred to them that their generosity would attract the attention of pagans from the northernmost regions of Europe.

Ironically it was English Christians who suggested—inadvertently—that England was ripe for Viking raids. English merchants, their purses fat with freshly minted gold and silver coins, had begun traveling to Scandinavian ports to purchase furs, walrus ivory, amber, and other valuable commodities they could sell back home. As they traded the merchants gossiped about the wealth of their towns, or the treasures in their churches, or the troubles their king was having with his unruly sons and ambitious nobles.

The Norse listened to these stories with interest. In Scandinavian society raiding an enemy’s farm or sacking a foreign town was a regular part of life. It introduced teenage boys to the warrior culture, gave men who spent most of the year farming and fishing a taste of adventure, and increased the wealth and reputation of the chieftain who led the raid. Stirred up by the English traders’ tales of great wealth “guarded” only by unarmed monks and helpless nuns, the Vikings readied their long ships for their farthest raiding voyage yet.

The attack on Lindisfarne was just the beginning. In 794 the Vikings looted Jarrow Abbey and the Isle of Skye; in 795 they made their first raid on Iona Abbey off the western coast of Scotland. A center of Celtic scholarship and culture, as well as the site of the shrine of St. Columba, Iona proved to be such a rich target that the Vikings returned again and again. In 806, after looting the church and chapels, the Vikings dragged almost the entire community of Iona—68 monks—down to the seashore and slaughtered them all. Ever since the spot has been known as Martyrs’ Bay.

After the 806 massacre, the surviving monks were unwilling to refound their abbey and expose themselves yet again to the fury of the Norsemen; they packed up what remained of their possessions and sailed to Ireland. By 825, however, once again there was a small monastic community on Iona. When rumors reached the island that the Vikings were raiding in the area again, most of the monks fled, taking the relics of St. Columba with them. A handful of monks, along with their abbot St. Blathmac, refused to go. One morning, not long after the main body of the monastic community had run off, the monks heard the dreadful sound of dragon ships skidding up on the sandy beach, followed by the fierce cries of a Viking raiding party as they leapt ashore. The raiders headed straight for the church where Blathmac was at the altar saying Mass, attended by the remaining monks. The monks the Vikings killed outright. Then, advancing on the abbot, they demanded that he reveal to them the hiding place of the treasures from St. Columba’s shrine. Blathmac refused. Raising their swords and axes the Vikings hacked St. Blathmac to death on the altar steps.

Initially Viking raids on England were hit-and-run affairs, but after the final attack on Iona in 825 they became more daring. They sacked and burned London, Canterbury, and Rochester, and they mounted a full-scale invasion of England with 350 dragon ships anchoring in the mouth of the Thames. Then, rather than returning home for the winter as had been their custom, the Vikings decided to stay. They occupied a huge portion of England that stretched from London almost to gates of Durham, far to the north. But what must have seemed to the English to be an unmitigated disaster had unpredictable consequences.

As the Vikings put down roots and began to intermarry with the English, these ferocious pagans began to convert to Christianity. No one saw that coming. Inspired by this sudden wave of new converts, English bishops and monks set out for Scandinavia to preach the gospel in the Viking homeland. And the faith began to flower there.

It wasn’t all smooth sailing. St. Olaf, the first Christian king of Norway, had an imperfect grasp of Christianity. He waged war against any of his subjects who would not accept baptism. After he died in battle against a pagan army, Olaf was instantly proclaimed a saint, martyr, and patron of Norway. Within a few years, Norse whose grandfathers had looted the shrines of saints were now going on pilgrimage to pray at the shrine of St. Olaf.

History is filled with examples of the mysterious working of divine grace in the world. But among the most astonishing is the transformation of the Vikings from bloodthirsty heathens into committed Christians.