Start with the ship, because the ship is why any of this happened.
Scandinavian shipwrights built by overlapping thin planks and riveting them, then fitting a light internal frame afterwards. The result is a hull that flexes with the sea instead of resisting it, weighs very little for its length, and draws almost nothing. Ships that had crossed open ocean could be rowed up a river until the water was a metre deep, run onto a beach, unloaded without a harbour, and dragged overland between waterways.
Excavated examples, several of them recovered nearly whole from burial mounds and from a deliberately sunk blockade in a Danish fjord, let us measure this rather than guess at it. Reconstructions sailed by modern crews have crossed from Denmark to Ireland and made speeds that surprised the people who built them.
Set that against what everyone else had. A European kingdom of the period defended itself by garrisoning strongpoints and mustering a levy, both of which take weeks. A force that can appear at any point on a coast or two hundred kilometres up a river, and be gone before the levy assembles, is not a military problem those states were built to solve.
One correction while we are here. No Viking wore a horned helmet. The helmets that survive are plain iron caps. The horns were put on stage by a costume designer for a Wagner opera in 1876 and have been impossible to remove since.
The conventional starting date is 793, when raiders sacked the monastery on the island of Lindisfarne off the English coast, and a scholar at the Frankish court wrote a horrified letter about it that survives.
As for why, there is no agreed single answer and probably no single cause. Several explanations are on the table and they are not exclusive.
Political consolidation at home. Kings were forming larger units in Norway and Denmark, and men who lost out in that process had ships, followers and no prospects.
Silver. Enormous quantities of Islamic silver coin have been dug out of Scandinavian and Baltic hoards, arriving via the Russian rivers, and the flow correlates with the raiding period. Once an economy runs on silver and status is bought with it, acquiring silver becomes the point of a career.
Targets. Monasteries were undefended, coastal, and full of portable metalwork, and Christian Europe had helpfully concentrated its treasure in buildings guarded by unarmed men. A first raid that goes unpunished advertises itself.
And technique. The ship made a kind of expedition possible that had not been possible before, and the political fragmentation of the Frankish empire described in the last chapter meant nobody could organise a coastal defence across the whole of it.
The word viking in the old languages is closer to an activity than a people: going raiding was something a Scandinavian might do for a few seasons, not what he was. Most Scandinavians in this period were farmers who never went anywhere.
And the expeditions that did go were as often commercial as violent, frequently both in the same voyage. Trading towns grew up around the Baltic and the North Sea handling furs, walrus ivory, amber, iron, soapstone, wool and wax.
The largest single commodity, and the one most often left out, was people. Raiding produced captives, and captives were sold. Dublin, founded by Norse settlers, became one of the major slave markets of western Europe, and the trade ran east as well, down the Russian rivers to Muslim buyers, which is where a good deal of that silver came from. Irish and English annals record the taking of populations, and Arabic writers describe the merchants arriving with their goods at the Volga.
This is the part of the story that fits neither the older picture of pure barbarism nor the more recent enthusiasm for Vikings as misunderstood traders. They were traders. One of the things they traded was human beings, and the demand was in the sophisticated societies at the other end.
West, first. England was raided, then invaded by a large army in 865, and within a decade three of the four English kingdoms were gone. The survivor, Wessex under Alfred, fought back to a stalemate, and the settled area under Scandinavian law in the north and east is remembered in the name Danelaw. Hundreds of English place names and a set of very ordinary English words, including they, them, egg, sky, knife, window and law, come from that settlement.
Ireland was raided and then settled at coastal points, and Dublin, Waterford, Wexford, Cork and Limerick all began as Norse towns.
In Francia the raids went up the Seine and the Loire repeatedly, and in 911 a king solved the problem by granting a Scandinavian leader the mouth of the Seine in return for defending it against other Scandinavians. Within a century and a half his descendants were speaking French, were the most formidable soldiers in Europe, and had conquered England and southern Italy. The name of the region records where they came from.
East, the traffic ran down the rivers of what is now Russia and Ukraine, trading and settling, and Scandinavian and Slavic elites merged into the polity that produced the states of Kyiv and Novgorod. Some went the whole way to Constantinople, where the emperors recruited them as a personal guard, and one of them left runic graffiti carved into a balustrade in Hagia Sophia which is still visible.
And out into the Atlantic: the Faroes, Iceland settled from the 870s, Greenland from the 980s, and, around the year 1000, a landfall in North America. That last was known only from two Icelandic sagas until an excavation in the 1960s at the northern tip of Newfoundland found Norse buildings, iron rivets and a smithy. It is a small site, occupied briefly, and it settles the question.
There is one Norse institution worth a section of its own, because it connects to the thread this book started with.
Free men met in periodic open air assemblies to make law and settle disputes. The word for such an assembly is thing, and it survives in the names of the Icelandic, Norwegian and Danish parliaments to this day. A thing was not a democracy in the Athenian sense; powerful men dominated it and the poor and the enslaved had no standing. But it was public, it was adversarial, and its decisions bound the men who attended.
The extreme case is Iceland, settled by people who had left Norway partly to get away from a king, and which then ran for three centuries without one. From about 930 an annual general assembly met on a rift plain in the south west. There was no executive, no police and no army. There was a law speaker, elected for three year terms, whose job was to recite a third of the law aloud each year from memory so that everybody knew it, and courts that heard cases and issued judgements.
The obvious weakness is that a judgement with nobody to enforce it is a suggestion. Enforcement fell to the winning party and his kin, which meant that verdicts against powerful men were hard to collect, and that feud remained the mechanism of last resort. In the thirteenth century the system collapsed into exactly the sort of warfare between a few great families that it had been designed to avoid, and Iceland submitted to the Norwegian crown.
It is still remarkable. For three hundred years a European society of some tens of thousands of people ran a legal system, resolved disputes, adopted Christianity by a formal vote of the assembly in the year 1000, and kept written records, without a state. And the law was written down early, in the vernacular, which is why we know as much about it as we do.
It stopped because the Scandinavians became the thing they had been raiding.
Kings in Denmark, Norway and Sweden consolidated their power over the tenth and eleventh centuries, and consolidation meant adopting the technology of European rulership: Christianity, which came with literacy, a church hierarchy answerable to the king, and a theory of anointed kingship; coinage struck in the king’s name; towns; and written law.
Conversion was gradual, top down and politically motivated, and the archaeology shows the two religions overlapping for generations, with pagan and Christian symbols in the same graves and on the same objects. Once it was done, a Scandinavian king was a Christian European monarch with the same interests as his neighbours, and the raiding of monasteries had become an attack on his own church.
The last act is 1066, which is best understood as a Scandinavian settlement of the English question. Three men claimed the throne: an English earl who had it, a Norwegian king who invaded in the north and was killed at Stamford Bridge, and the duke of Normandy, a descendant of the settlers of 911, who landed in the south three days later and won at Hastings against an army that had just marched two hundred and fifty miles.
The English side of that year is worth one more sentence, because it shows how completely the Scandinavians had been absorbed. The duke who won at Hastings was the great great great grandson of a Norse warlord, and he arrived speaking French, fighting on horseback in the continental manner, and carrying a papal banner.
By 1100 Scandinavia was a region of ordinary Christian kingdoms sending bishops to church councils, and the age was over.
Firm: the archaeology, which is unusually good. Ships, houses, towns, graves, hoards, workshops and the Newfoundland site are physical evidence independent of anyone’s account. Coin hoards let us track silver flows by decade. Isotope and DNA work on burials is now showing where individuals grew up.
Firm: the linguistic residue. Place names and loanwords map the settlements more reliably than any chronicle.
Very soft: the narrative sources. Contemporary written accounts are almost entirely by the victims, in monasteries, whose houses were being burned and who had a theological reading of it as divine punishment. The Scandinavian side of the story comes mainly from Icelandic sagas written in the thirteenth century, two hundred years and more after the events, in a Christian society, as literature. They preserve real tradition and they are not reportage.
Contested: the scale. Older scholarship took the chronicles at face value and imagined vast fleets and mass migration. A revisionist wave argued for small warbands and modest settlement. Genetic and isotopic studies have since pushed back towards substantial movement in some regions, particularly the north of England, and the argument continues by region rather than in general.
Contested and worth knowing: a richly furnished warrior grave at Birka in Sweden, long assumed to be male, was shown by genomic analysis in 2017 to be biologically female. The finding itself has held up. What it means, whether the person was a warrior, whether the objects indicate a role or a status, is genuinely disputed among specialists, and both the confident claims and the confident denials in the popular coverage went beyond the evidence.