What Caused the Viking Age?
That they appeared suddenly in the historical record has launched historians, archeologists, and various fields of science on a quest to answer the question: What caused the Viking Age?
The causes of the Viking Age are a topic my co-host Terri Barnes and I have discussed at length on our podcast Vikingology.
On June 8, 793 A.D., the world of Christendom changed forever. A fleet of mysterious ships appeared off the coast of Northumbria and took aim at the island monastery of Lindisfarne. The Anglo-Saxon Chronicle records:
"In this year terrible portents appeared over Northumbria, and miserably frightened the inhabitants: these were exceptional flashes of lightning, and fiery dragons were seen flying in the air. A great famine soon followed these signs; a little after that in the same year on 8 [June] the harrying of the heathen miserably destroyed God’s church in Lindisfarne by rapine and slaughter."
In The Two Lives of Charlemagne, by Notker the Stammerer, the emperor of the Carolingian Empire allegedly bore witness to an early raid attempt off the coast of France. So the chronicler tells us when the Northman ships learned Charlemagne and his army had made camp near their target, they turned back and fled. They may not have inflicted any harm to the coast of France on that day, but their sudden appearance and disappearance deeply unnerved the most powerful man in Western Europe of the day. Notker further wrote:
“Charlemagne, who was a God-fearing, just and devout ruler, rose from the table and stood at the window facing East. For a long time, the precious tears poured down his face. No one dared to ask him why. In the end, he explained his lachrymose behavior to his war-like leaders. ’My faithful servants,’ said he, ‘Do you know why I wept so bitterly? I am not afraid that these ruffians will be able to do me harm, but I am sick at heart to think that even in my lifetime they have dared to attack this coast, and I am horror-stricken when I foresee what evil they will do to my descendants and their subjects.’”
Most historians question whether Charlemagne did in fact witness such an event, but the message conveyed to us by Notker is clear: the Vikings posed a real danger to the coastlines of Western Europe even before the accession of Louis the Pious. The terror they struck in the hearts of their victims paints a picture of a threat that no one in Christendom had predicted.
The first recorded attacks at Lindisfarne in 793 A.D., in Ireland in 795 A.D., and in France in 799 A.D. are widely considered the beginning events of what historians call the Viking Age. Though the Viking Age lasted for nearly three centuries, the initial raids between the years A.D. 793 and 835 occurred peripherally, meaning they remained contained to coastlines (in contrast, the second half of the 9th century was marked by invasion attempts and conquests). This is the period that is most romanticized in popular culture: longships filled with rugged bands of marauders suddenly appearing on the horizon to sack and loot monasteries for their silver. That they appeared suddenly in the historical record has launched historians, archeologists, and various fields of science on a quest to answer the question: What caused the Viking Age?
Most historians draw upon a combination of several hypotheses to explain the cause of the Viking Age. These hypotheses range in scope from territorial disputes to diplomatic tensions with neighbors, and nearly all of these factors seem to have played a part. Not unlike Europe on the eve of World War I, Scandinavia in the late 8th century appears to have been ready to boil over, and all the situation needed was a catalyst. Unfortunately, attempts to define a single catalyst or trigger event have all proved unfruitful. A 2010 paper by the archeologist James Barrett called such attempts “unrealistic” and proposed the start of the Viking Age could only be defined by combining numerous factors into a broader, more general theory.
What caused the Viking Age? The best we can say is that it was a combination of numerous factors, including climate change, trade, political strife, and social stratification. Here, I will explore a few that served as likely significant contributors to the Viking Age's start.
New Technology: The Longship
One of the more compelling hypotheses proposed to explain the onset of the Viking Age rests on technological determinism. In this view, the Vikings did not leave home because they were driven to by desperation, overpopulation, or political pressure, but rather because, at a certain point in the eighth century, they could. Something changed in their technological toolkit that suddenly made long-distance raiding and exploration possible. According to this school of thought, the moment that changed everything came when Scandinavian boatbuilders learned to lay down a keel.
Before the late eighth century, Scandinavian watercraft largely resembled the Hjortspring boat—a pre-Roman Iron Age vessel dated to around 400 B.C. Found in a bog in Denmark, the Hjortspring boat was constructed from sewn planks, with no keel and little capacity for open-sea travel. It was suitable for lakes and calm coastal waters, but not for the kinds of voyages that defined the Viking Age. Over time, Scandinavians improved their shipbuilding techniques, developing clinker-built vessels. The term “clinker” refers to the overlapping method of attaching planks along the hull, which created a flexible and strong structure. This method allowed ships to absorb the energy of rough water better, making them much more seaworthy.
The true innovation came with introducing a long, central spine running the ship's length beneath the hull, also known as a keel. This addition provided greater directional stability, which enabled Viking ships to cut across open water more efficiently and with greater control, and the ability to stand up a much larger sail, allowing for more distant ocean travel. The Viking longship became one of the most advanced seafaring vessels of its time. These ships could travel at high speeds with either oars or wind power and could navigate open seas and shallow rivers. They were fast, agile, and could appear unannounced anywhere and anytime. They were the ideal tools for both raiding and escape.
The Skuldelev ships, excavated in Roskilde Fjord in Denmark, offer us the most direct window into these innovations. Scuttled in the 11th century to block a channel and protect against naval invasion, these five ships were remarkably well preserved. They include longships built for speed and war, and broader merchant ships designed to carry cargo across great distances. Among them, Skuldelev 2 is a warship built in Dublin around the mid-11th century and likely crewed by 60–70 men. Its deep keel and clinker-built hull embody the full maturity of Viking shipbuilding. A modern reconstruction of Skuldelev 2, named Sea Stallion from Glendalough, reached speeds of up to 17 knots during sea trials, which is impressive even by today’s standards.
From this angle, the rise of Viking expansion resembles other historical cases in which technological breakthroughs unlocked rapid territorial growth. The Mongols, for instance, changed the shape of the medieval world by perfecting cavalry tactics built around a seemingly simple innovation: the stirrup. This device allowed horsemen to shoot while riding and dramatically increased the effectiveness of mounted warfare. Similarly, the keel and clinker-built construction may have given the Norse an edge, turning them from regional seafarers into transcontinental raiders, traders, and colonists.
The evidence is compelling from a practical standpoint. Without these ships, the Viking Age as we know it could not have happened. The raids at Lindisfarne, the siege of Paris, and the voyages to Iceland, Greenland, and Vinland would have been unthinkable. These vessels were instruments of war, symbols of status, and cultural artifacts in their own right. They enabled an entire way of life. The longship was as essential to the Viking identity as the sword or the saga.
But here is where the theory begins to unravel. As archaeologist James Barrett points out in his 2010 paper, the technological developments that made Viking expansion possible long predated the beginning of the Viking Age. Keel-based, sail-driven ships existed in Scandinavia at least several decades—possibly a century—before the attack on Lindisfarne in 793.
Ultimately, the longships only explain how the Vikings left home, not why they chose to do so.
Climate Causes
For as long as the study of the Vikings has existed, historians have proposed a short period of climatic warming as a primary longue-durée cause of the Viking Age. Indeed, most books about Viking history will include some variation of the hypothesis. While not a catalyst for the events of the late eighth century, the warming period may have contributed to societal developments in Scandinavia that caused societal duress during the ensuing cooling period.
The long-term effects of climate, however, have come under scrutiny from several camps. A 2013 study by the historians Morgan Kelly and Cormac Ó Gráda argues too little evidence exists to correlate climate with social and political changes in the early medieval period. They acknowledge the impact climate change would have had on medieval society if it were a provable phenomenon, but stress that more research must be conducted to keep the climate hypothesis alive.
Social and Cultural Causes
Several leading theories on what caused the Viking Age focus on the social causes born from early Scandinavia’s stratified society and warrior culture. In a 2015 paper, historian Steven Ashby proposed social capital acquired through fame and glory drove sea captains to raid abroad. In the article, he writes, “In the flexible hierarchies of the Viking Age, those who took advantage of opportunities to enhance their social capital stood to gain significantly. The lure of the raid was thus more than booty; it was about winning and preserving power through the enchantment of travel and the doing of deeds. This provides an important correction to models that focus on the need for portable wealth; the act of acquiring silver was as important as the silver itself.”
Other social traditions may have also played a significant role in encouraging young men to raid abroad. The bride price — the price paid by a man to a woman’s family for her hand in marriage — may have precipitated the desire by young men to join sea captains on raids. The treasures they brought home would have paid the bride price for the woman they wanted to marry. In a 2017 paper, historians Ben Raffield, Neil Price, and Mark Collard proposed operational sex ratios driven by polygyny and concubinage led to the need for young men to seek treasures abroad to afford the bride price and increase their chances at marrying.
Political Causes
In 782 A.D. Emperor Charlemagne was just wrapping up his conquest of modern-day Poland when the Saxons, under the leadership of a man named Widukind, rebelled against him. According to the Royal Frankish Annals, Charlemagne’s response was swift and bloody. During their battle near the Elbe River, the Franks took 4,500 prisoners. To teach the rebels a lesson, Charlemagne ordered the prisoners be baptized in the Elbe. The priests recited their benedictions, and the Frankish soldiers held their victims underwater until they drowned.
The event, after that dubbed “The Massacre of Verden” was no more gruesome than many of the other acts committed by the Carolingians. Forced baptisms and conversions were commonplace under Charlemagne’s rule. But Verden was different. The leader of the Saxons, Widukind, was brother-in-law to the king of the Danes, Sigfred. News of the massacre undoubtedly reached the Danish court, and as such would have (and this is conjecture) deeply angered them. It was yet another brutal, violent display of power by Charlemagne, the latest in a long series spanning decades.
Danish raids along the coast of Frisia (modern-day Netherlands) appear to have intensified almost immediately, leading to an infamous assault on the important trade port of Dorestad. The very next decade, an attack on Lindisfarne occurred, and what happened there has led some to believe that there may have been a connection between the two. A source on the attack by the twelfth century English chronicler, Simeon of Durham, who drew from a lost Northumbrian chronicle, described the events at Lindisfarne this way:
“And they came to the church at Lindisfarne, laid everything to waste with grievous plundering, trampled the holy places with polluted steps, dug up the altars and seized all the treasure 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…“
Some have proposed the drownings symbolized the forced baptisms at Verden. The evidence, however, is inconclusive. What is undeniable is that interactions between the Danes and the Franks, and the kingdoms of the British Isles, predated the official start of the Viking Age. Political strife may have served as an important trigger.
Trade
More recent scholarship on the subject of trade has revealed less apparent causes for the start of the Viking Age. A 2018 study by Irene Baug, Dagfinn Skre, Tom Heldal, and Øystein J. Jansen examined the location and provenance of whetstones to establish probable trade ties between geographic regions across the Baltic region. Most of the whetstones analyzed originated from the settlements of Lade and Borg in what is today Northern Norway. Dating of the quarry sites and the stones reveals the whetstone trade had likely established ties between these remote regions of Scandinavia and the more urbanized southern Baltic regions, such as Ribe, as early as the beginning of the 8th century. The study authors offer further evidence of these ties by citing the discovery of a reindeer antler comb from Norway found in Ribe, Denmark that predates the presupposed timeline for the establishment of trade.
If trade between Lade and the English Channel, even if not direct, had been established in the 8th century, the resulting contact from that trade could have inspired sea captains to shift their focus from trading to raiding, as was often done when the latter proved more worthwhile. As the study authors note: “This evidence, set in the context of the contemporary surge in production and trade around the southern North Sea and English Channel, the early urbanisation in southern Scandinavia and the Baltic, and the political integration in southern and western Scandinavia, allows us to suggest immediate reasons for why Viking ship commanders turned their activities overseas in the late 700s. The evidence also sheds light on why, after the initial ‘scouting phase,’ raiding in three decades since c. 806 took place predominantly in Ireland and Scotland, and why Vikings in the mid-830s began overwintering overseas and took up raiding in England and the Frankish Empire.”
Salt and Slaves, and the Eastward Expansion of the Rus
While Anglo-centric historians have defined the Viking Age as having started roughly in 793 with an event in England, recent scholarship has accepted that the Viking Age started much sooner in the East. A treasure trove of silver coins from the Muslim world found at Lake Ladoga gives us some idea of when contacts may have begun. As a standard practice in the Muslim world, coinmakers imprinted minting dates on their coins, and the coins at Lake Ladoga date to the 780s.
Primary sources for the early societal structure, culture, and activities of the Swedish Vikings, known as the Rus, are practically non-existent. They did not leave us any written sources besides disparate runes carved into wood planks or stones. One mention in the Annals of St. Bertin tells us of a diplomatic delegation from Constantinople that visited Louis I in Aachen in 839 that included Rus. Still, we have no other historical sources predating that mention. Thus, we must turn to archeological evidence.
Combined with further archeological evidence of pre-Viking Age colonies on the eastern shores of the Baltic, such as the Grobin colony in what is now Latvia, trade contacts between Sweden and the Middle East appear to have begun several decades before the Danes and Norwegians launched their first raids against the British Isles and France. Those early contacts appear not to have been violent, either. The earliest graves from the Grobin colony (pre-800s) include women and children, signaling a peaceful colonization effort, whereas later graves (mid-800s and later) contain fighting-aged men and their weapons.
Why the eastward expansion transitioned from trading to raiding remains a complex question with no precise answer. However, they may have been victims of their own success. Of all the longue-durée causes that contributed to the genesis of the eastward expansion and, by extension, the westward expansion, Søren Sindaebek’s synthesis on the role of the silver economy, urbanism, and the movement of durable goods as primary drivers perhaps has the best grasp on solving the mystery. Sindaebek and other historians have stressed at length the importance of the social bonds of the nuclear family, as well as the value of establishing familial ties, leading to a silver economy attached to the cultural practice of the bide-price. As Sindaebek wrote in a 2010 essay:
“My suggestion is, then, that a major motivation or affluent Scandinavian peasants to engage in long-distance exchange – and thus to enter into a silver economy – was that products acquired in this way could ease some of the most controversial issues of their social networks: the negotiations over the longterm status and personal property with which spouses, women in particular, entered into marriage. The incentive for trade and raids alike, I suggest, was ultimately driven by the hubs of family relations: by marriage and the negotiations or the families connected with it.”
Sindbæk, S. M. (2016). Urbanism and exchange in the North Atlantic/Baltic, 600–1000 ce. The Routledge Handbook of Archaeology and Globalization. T. Hodos, A. Geurds, P. Lane et al. Abingdon, Routledge.
If silver was a fundamental linchpin in the proper functioning of cultural practices that held together nuclear families, silver’s value was paramount to the fabric of society. Value, as economists insist, depends on supply and demand. Therefore, the amount of silver in circulation and its demand had dire consequences for the stability of Viking Age Scandinavian society. Where the supply and demand for silver had remained more or less constant in the two centuries leading up to the Viking Age, an increase in trade in the East threatened to unravel the delicate balance of pre-Viking Age Scandinavia.
Like the economic woes of the 16th century that resulted from the inflationary effect of Spain’s imports of gold from the New World, the influx of Islamic silver may have caused a significant devaluation of silver in Scandinavia. That effect would have had far-reaching consequences even in the most rural settlements. Given the role of silver in early Viking Age Scandinavian society, a sudden shift in the value of silver across Scandinavia may have threatened the most fundamental ties of the nuclear family. In simpler terms, the bride price got too expensive (like housing today).
The theory here, then, rests on the idea that Scandinvians to the west of the Swedes suffered from the influx of islamic silver, and so had to turn to other forms of portable wealth to compete. In my own research, I have made the case that salt was an important and oft-sought resource, as well as slaves. Check out my article on the Salt Hypothesis to learn more.
Of course, there is an assumption here that the silver economy held a kind of primacy in the factors that created the conditions for the Viking Age to begin, which is still widely debated. It is important to understand–and I will continue to stress–that all of the factors discussed herein are part of a much larger tapestry of themes and events, none of which constitute any kind of trigger.
Bringing it all together: What caused the Viking Age?
No single event or trend caused the Viking Age. Why sea captains and their crews launched from Scandinavia to raid abroad has its roots in a wide breadth of social, political, environmental, and cultural trends. Much more research is needed to peel back the shroud of mystery surrounding why longships appeared so suddenly off the coasts of England, Ireland, and France in the late 8th century.