They came out of the cold and hostile north on a June day in 793 A.D. - long, low, black ships with large, curving prows and broad, red-and-white sails, dancing over the waves toward the English tidal island of Lindisfarne off the coast of the medieval kingdom of Northumbria. The ships plunged right onto the beach, and out poured a band of mighty, tangled-haired men, howling like animals and waving their long, broad swords. They charged up the island’s grassy slopes, where sheep and cattle grazed.

Lindisfarne had much to attract the invaders. On the island stood a venerable Christian monastery to which generations of sinners had bequeathed riches for the salvation of their souls. In its chapels and on its altars lay a bounty of gold crucifixes, linen and silk tapestries, and books encrusted with jewels.

To the monks who lived amongst these treasures, the monastery was more than a repository of worldly wealth. It was a center of learning, a sanctuary for contemplation. The monks spent their days praying, chanting, inscribing manuscripts, corresponding with fellow monks throughout the Christian world, and chronicling the events of their times. They had no weapons to defend themselves, and they could not believe that anyone on the island would try to harm them.

The monks were no match for the intruders from the sea. These men had no reverence for the Christian God, no scruples about plundering a Christian sanctuary, and no regard for human life other than their own. They cut down some of the brothers in front of their altars. Others were thrown into the sea to drown, and still others were stripped naked and driven out of the monastery to hoots and jeers. The sacred buildings were looted - their gold and silver, illuminated manuscripts, and precious stones carried down to the beach, where the invaders loaded the treasures onto their waiting ships. Long before an alarm could be sent out, the vessels, now laden with plunder, vanished over the dark waters of the North Sea from whence they came.

This was an atrocity unprecedented in the memory of people of the time, and the shocking news flew as fast as messengers on foot, horse, and ship could carry it throughout the scattered Anglo-Saxon kingdoms in the south and east of Britain and beyond. Before long, knowledge of the event had crossed the English Channel to the land of the Franks on the Rhine. There another Anglo-Saxon monk and ranking scholar of the age, Alcuin, was supervising a revival of learning at the court of the Emperor Charlemagne at Aachen. Expressing his alarm, Alcuin wrote, “It is nearly 350 years that we and our fathers have inhabited in this most lovely land, and never before has such a terror appeared in Britain as this that we have just suffered from a pagan race.” To Alcuin and his contemporaries, the desecration of the monastery was not only appalling but remarkable - remarkable that at a time when sailors would not venture out of sight of land “such an inroad from the sea could be made.”

Alcuin could not have imagined the terrors yet to emerge out of the sea during his lifetime and many lifetimes to come - terrors that would make Lindisfarne seem like a minor act of vandalism. The pagans to whom he referred were the Norsemen, people with whom British and European merchants already had a nodding acquaintance as traders. Soon these raiders would be known as the Vikings and viewed as a scourge to the civilized world. In the Vikings’ melee of death and destruction, many like Alcuin saw the fulfillment of the words of the Old Testament Prophet Jeremiah - “out of the north evil shall break forth upon all the inhabitants of the land” - and thought the Day of Judgment might well be at hand.

The summer after the assault on Lindisfarne, the Vikings descended upon Jarrow, about fifty miles down the Northumbrian coast, and struck a blow at the monastery that once was the residence of the Venerable Bede, perhaps the greatest historian, theologian, and astronomer of his time. In the summer of 795, the Vikings ravaged Iona, off the coast of Scotland, and Morgannwg, on the southern coast of Wales. In 797, it was the turn of the Isle of Man, and, in 800, of a monastery just south of Jarrow, and another, more distant, on the west coast of Scotland. Before long, it was said, the monastery chapels and village churches of England rang with a new prayer: A furore Normannorum liberu nos, Domine (“From the fury of the Northmen deliver us, 0 Lord”).

And still the Northmen came. Those sudden, hit-and-run, summertime assaults at the close of the eighth century were just the first stirrings of what was to become an epic campaign lasting nearly 300 years. From about 800 onward, the Vikings swept south, west, and east as if on a tidal wave - swelling in numbers and spilling farther and farther afield. “The wild beasts,” wrote the French monk Abbo, “go through hills and fields, killing babies, children, young men, old men, fathers, sons, and mothers. They overthrow, they destroy, they ravage; sinister cohort, fatal phalanx, cruel host.”

Sometimes the Vikings struck the same places again and again. The famous Irish monastery of Armagh - chosen by St. Patrick as the base of his church in the early fifth century - was to be plundered five times - three of them in one month in 832. The port of Dorestad, on the Rhine, the biggest commercial center of northern Europe, was robbed, wasted, and depopulated at least six times. No one knew where the Vikings would strike or when or in what numbers. Hamburg was sacked. Paris was burned. As fear and foreboding enveloped Europe, “it seemed,” wrote one monk, “that all Christian people would perish.”

The Irish author of a dire twelfth-century book entitled The War of the Irish With the Foreigners spoke for all Europe when he cried out from the depths of anger and anguish: “Although there were a hundred hard, steeled, iron heads on one neck and a hundred sharp, ready, cool, never-rusting, brazen tongues in each head and a hundred garrulous, loud, unceasing voices from each tongue, they could not recount, or narrate, or enumerate, or tell what all the Irish suffered in common, both men and women, laity and clergy, old and young, noble and ignoble, of hardship and of injury and of oppression in every house, from these valiant, wrathful, purely pagan people.”

Such was the picture of the Vikings drawn by monks. Yet, Vikings had another side. It was one that worried monks could not see or recognize - a hugely productive and creative side. And in the long run, this aspect was far more consequential than all the fire and fury of their raids and incursions.

The Norsemen may have begun as raiders, but they developed into skilled conquerors and competent administrators. They established long-lived states at the ends of Europe - east, west, and south. They taught the wild Slavic people of what is now Russia the rudiments of civil government. The Duchy of Normandy in northern France was a Viking creation that, by the standards of the time, was a model state with a more tightly centralized government than anything the West had seen since the overthrow of Rome centuries before.

The Vikings were capable tradesmen as well, canny, enterprising, risk-taking merchants, always on the lookout for new routes of commerce to open or old ones to revive. They brought fresh goods and fresh ideas to the West and played a pivotal role in spawning the new class of feudal lords that would arise in the Middle Ages.

Although they came from an almost entirely rural society with no more than a few towns in all their land, they became town builders when the occasion demanded. Plundering the primitive agricultural kingdoms of Ireland, they found it advantageous to create a series of market towns all around the coasts that became cities and, for the first time, provided the Irish with the inspiration and challenge of urban life.

The Vikings were foot-loose, adventurous, and brave as lions, all qualities that made them desirable mercenary soldiers for foreign rulers. When the ruler himself was brave and generous, they fought for him to the death. Vikings formed the personal bodyguard of the Roman emperors of Byzantium and helped their doomed but dazzling realm to survive for another half millennium.

All this the Vikings could achieve because they were the most mobile people of their age, masters of those greatest of highroads, the seas and rivers and lakes. The Viking genius was born of water. They were never more at home than when scudding along distant courses in the ships they had built with immense thought and craftsmen’s attention, the fastest and finest vessels the world had ever known.

At their most daring, they took these superb ships out across the Western oceans into waters where, so far as they knew, no one had ever sailed. And when they found empty lands in the northern waters, they turned into persistent colonists. In desolate Iceland, they built the first republic of modern Europe, and then they ventured far beyond to become the first Europeans to set foot on the vast ice-capped mass of Greenland and on the more appealing shores of North America.

Much about these lusty, feisty, inquisitive, wide-ranging adventurers remains a mystery - including the very name by which they are known. No one is sure where the word Viking came from or what it originally meant. Various etymologists have traced it to various Old Norse words - from vik, meaning “inlet,” because the Vikings’ Scandinavian homeland was riven by fjords; from vig, meaning “battle,” because they were so skilled in making wars, and from vikja, meaning “to turn aside, to deviate,” a comment on their wiles and wanderings.

Whatever its origin, the word quickly acquired for the peoples of Europe a meaning it has never lost: a seaborne rover, raider, and conqueror, full of courage, guile, and brute strength. It meant much the same to the Vikings themselves. When a Norseman said he was “going a Viking” - as bold and ambitious men in the Scandinavian lands dreamed of doing throughout the ninth and tenth centuries - he meant that he would equip a ship to sail over the high seas in search of plunder and adventure. Both of these to the Vikings were eminently respectable goals. Yet, there was always an ambiguity about the term. Vikings were just as likely for one reason or another to turn their prows against their own neighbors as against distant foreigners. And when they did, those who had been harmed would scour the seas to punish them. Once a party of Vikings settled down and made a territory their own, they did not like being preyed upon any better than anyone else. Earl Magnus, a Viking born in the Orkney Islands in Northern Scotland, was praised in a saga as being “severe and unsparing” toward robbers and sea raiders.

The origin of the name Viking is only the first of the puzzles associated with the Norsemen. Virtually everything that is known about them comes from vague and incomplete ancient sources and from modern archeology, which has only begun to piece together their history.

The most nearly contemporaneous of the written sources are the manuscripts of the clerics, such as those of Alcuin, Abbo, and Adam of Bremen. Their writings, combined with secular histories like the Anglo-Saxon and Russian chronicles, present hundreds of firsthand commentaries and reports. But at the same time, these records are likely to be biased since they were written by the victims of the Vikings or by partisans of the victims. Other written accounts were left by acquaintances of the Vikings, such as the Arab merchants who encountered them in marketplaces around Scandinavia and continental Europe. But these proud Muslims were not much more favorably disposed toward the Vikings than were the Christian monks. Coming from an infinitely more settled society, they looked upon the Vikings as crude and uncouth. “They are the filthiest of God’s creatures,” wrote the Arab traveler Ahmad ibn Fadlan. “They do not wash after discharging their natural functions; neither do they wash their hands after meals. They are as stray donkeys.”

Alas, the Vikings themselves kept neither logs at sea nor ashore. Until the eleventh century, they rarely wrote anything except runic inscriptions on grave and crossroad markers. The only surviving accounts in their own language are the sagas - the legends of their heroic age, which were transmitted orally from generation to generation and not written down until long after the Viking age had ended.

However, the sagas are a treasure-trove of information. They reveal much about how the Vikings lived, loved, worshipped, waged war, hunted, traded, and explored. And the picturesque names by which they knew their epic figures conjure up much about their character and their behavior: King Eric Bloodaxe and Thorfinn Skullsplitter, known for their prowess in battle; Onund Treefoot, who had a leg cut off in a sea battle and stumped around on a wooden one thereafter; Olaf Peacock, who loved fancy clothes; and Sigurd Sow, who, although he was a king, dressed in old clothes and was always rooting around in his fields like an ordinary farmer.

As might be expected with histories committed to paper centuries after the fact, the sagas are riddled with contradictions, ambiguities, and mystifying obscurities. The authors often tended to be maddeningly brief and matter-of-fact about the most notable of events. Nevertheless, for all their shortcomings, the sagas remain the truest sources for understanding the values the Vikings lived by and for viewing their heroes and villains through their own eyes. Moreover, archeology has confirmed some of what the sagas recount - as it has the events recorded in the Christian chronicles.

At the dawn of the ninth century, when they began their raids on coastal Britain, the Vikings, who erupted out of Scandinavia, were essentially one people. They were then barely on the brink of dividing into the three nations of Denmark, Norway, and Sweden. They spoke the same language, Old Norse. They lived the same rough life on isolated farms, usually near a body of water. They worshipped the same gods, and their bards sang the same songs to honor the same warrior ancestors.

They were descended directly from the Germanic tribes that fanned out over continental Europe between the first and fifth centuries A.D. and brought down the Roman Empire. But earlier ancestors of the Norsemen can be traced much further back to 6000 B.C. By that date, men and women were paddling in makeshift crafts among Denmark’s 600 islands into the deep, narrow fjords that cut from the sea through Norway’s craggy mountains and over the thousands of lakes and rivers that lace Sweden. The people who used these vessels were nomads moving from one hunting ground to another. Presumably, they paddled offshore in pursuit of seal, porpoise, and whale.

Two millennia later, these nomads were joined by a new wave of migrants and settled down to sow crops and live in permanent dwellings, but, still, hunting from boats provided their main form of food, which was fish. By 1500 B.C., they had loaded their crafts with flint tools and Baltic amber - some of it worked into jewelry, some of it raw. They ventured as far as Britain and Ireland to barter for gold, copper, and tin. No oceangoing vessels of that period have been found, but goods, unquestionably Scandinavian, have been uncovered in the British Isles.

Paradoxically, the seas and fjords that from time immemorial inspired the Scandinavians to build boats - thus making possible both travel and communication - simultaneously bred in them traits of separateness and regional pride. Living in isolated pockets of land - where they wrested a living from an ungenerous, rock-strewn, and often frost-bound earth - they developed proud independence and fierce loyalties to their communities.

A Viking farmstead cultivated oats, barley, rye, and cabbage to supplement the catch from the sea, and it raised flocks of geese and herds of cattle, goats, pigs, and sheep to provide both food and raw materials (feathers, horn, skin, and wool) for tools, clothing, and the boat that was sure to be among its goods and chattels. On the farmstead stood a large building that perhaps housed as many as a dozen people, including two or three slaves, who labored as farm hands and general helpers. The house might be faced with timber, stone, sod, or wattle and daub, depending on what materials were at hand.

Indoors, benches lined the walls of the central hall. The center seat was often raised to create a sort of throne of honor, and it was flanked by two pillars that were more symbolic than practical. The sagas claim that all of the indoor woodwork (and especially the high-seat pillars) was heavily carved, often with geometric and floral designs and sometimes with representations of a deity such as the ever-popular, hammer-wielding Thor. In such a hall, presiding in his high seat and surrounded by his sons and followers, sat the bondi. He was the self-sufficient patriarch and proprietor of the farm.

A Viking community might have a group of such houses huddled together, village fashion, or it might have some scattered over a valley that reached from the waterside to a mountain boundary. In either case, the community was predominantly populated by a family or several families, who were related down to third cousins, even fourth cousins - people who shared a common great-great-great-grandfather.

These extended families formed federations with other extended families that occupied neighboring territories. Such federations shared hunting and fishing, defense and trade - and as the practice grew after the end of the eighth century raiding into foreign lands. Each extended family had its chieftain, known as a jarl, or “earl,” and, in times of stress, natural leaders emerged from among the chieftains. Such a leader might be known as a konungr - Old Norse meaning literally “man of noted origin” and related to the English word king.

In the early Viking days, such a minor king was by no means a national monarch. He was merely the central figure in his region, large or small. Denmark, Norway, and Sweden began to emerge only after the strongest of these minor kings had subdued and unified a number of lesser kings and jarls, often after long and fierce fighting. Not until the middle 870s, some eighty years after the raid on Lindisfarne - did Norway acquire a king in the person of Harald Fairhair. Denmark and Sweden lagged more than a hundred years behind Norway, with Svein Forkbeard ascending in Denmark in 985 and Olaf Skotkonung coming to rule Sweden in 993. Even then the boundaries of the three nations continued to shift far after the Middle Ages, and the role of the kings themselves depended upon the acceptance of their people - or their own strength and skill in forcing that acceptance.

A Viking leader, whether a king leading an invasion or a jarl instigating a local brawl with another chieftain, was expected to be in the forefront of the fight and to perform feats of strength beyond the capacities of other men. Bloodthirsty, greathearted Olaf Tryggvason, who ruled a part of Norway at the close of the tenth century, was one of the most admired Viking kings. One reason, as the saga devoted to his life says, is that he could hurl two spears at once, one with each hand, and jump over the gunwale of his immense, dragon-prowed ship and leap from oar to oar while his men were rowing.

In the early days, it was a rare occurrence for a ruler to succeed in passing his crown to a son unless that son was prepared to fight for the right to keep it. The Vikings had no long-established aristocracy. The bondis recognized only force of will and arms. As free men and warriors as well as farmers, many among them nurtured ambitions of becoming jarls or even kings.

The dominant preoccupation in a bondi’s life was family. His first duty was to his relatives. His primary aim was to increase their wealth and prestige and to defend their honor against the greed and affronts of others. That honor might be challenged any time a quarrel broke out and over any pretext: the size of a dowry, the theft of a sheep, the rights to a stranded whale. Such a challenge demanded satisfaction. Thus, blood feuds were part of the normal pattern of the Norseman’s life.

At any moment, say the sagas, the daily round of farming, herding, and fishing might be torn asunder. A single spark of violence might set off an endless succession of duels, ambushes, pitched battles, murders, maimings, and burnings. These blood feuds were pursued with deadly intensity as each fresh killing stoked the hatred. “I would ask this of you, that you forgive me for whatever I have done against you,” said Thord Andreassson in a saga when he had fallen into the hands of his enemy, a jarl named Gizur. “That I will do as soon as you are dead,” replied Gizur in the cold, dispassionate tone that had been his since the day his entire family had been massacred by Thord and his friends. Thord tried to break away but was felled by an axe stroke in the back of the neck delivered by one of Gizur’s followers.

Anyone stood ready to help sustain a feud - even a king. Another saga tells how one day at the court of King Magnus the Good of Norway, Asmund Grankelsson, one of Magnus’ men looked down to the harbor and saw his enemy Harek of Thjotta alighting from his ship. “I will pay Harek for my father’s murder,” cried Asmund, brandishing his weapon, which was only a slight kind of hatchet. “Rather take this axe of mine,” the King said to Asmund, “there are hard bones in the old fellow.” And he gave him a thick axe with a handle like a club. Asmund took it without a word, went down and plunged it into Harek’s skull with such ferocity that the axe edge was bent by the blow.

The Viking woman was raised to be the mate to such a man. She had to be durable and self-reliant, for she might have to assume responsibility for family and farm while her husband was away fighting or seafaring. And she was a stickler for family honor - understandably, for there was hardly a Viking woman who had not seen a father or brother or husband carried home broken and bloody from a fight. Unlike the men, she did not bear arms and could not take out her grief and rage in physical violence. But she could insist that the men return her an eye for an eye.

A saga recounts how an Icelandic chieftain named Flosi made an unusual attempt to stop the killings between his family and that of a neighbor named Njal. Flosi had been willing to accept a payment of money in atonement for the murder of his niece’s husband Hoskuld. But his move to pacify the quarrel got him nowhere. His widowed niece Hildigunn taunted him with being a coward and threw at him the terrible, blood-clotted shirt in which her husband had been slain. She goaded Flosi into slaughtering Njal and all his sons. That act, in turn, led Njal’s son-in-law to take threefold revenge on Flosi and his family and friends. There seemed to be no way to end such feuds; they went on and on in perpetuity - or until one family was totally wiped out.

The sagas make so much of the incessant feuding and bloodletting that it is a wonder the Vikings had any energies left to work their farms - to say nothing of joining forces to raid abroad. Possibly the ancient storytellers gave an exaggerated idea of the extent of the feuds, although they were certainly a large factor in Viking life.

In any case, death held no terrors for the Viking warrior. If he fought with valor, he could expect to be summoned by the god Odin to join his fellow heroes in the golden, celestial realm of Asgard, the capital city of the Norse Gods, and live in the great hall of Valhalla, where a man could feast and fight forever. The Viking gods who presided over the heavenly and earthly arenas were lusty fellows cast from the same rough mold as the Vikings themselves. Leading the pantheon was Odin, the one-eyed magic god of wisdom, war, and frenzy - a spirit of great cunning and bravery, protector of chieftains and poets alike. Then there was Thor, a stormy-tempered redhead who, as a slayer of giants and ruler of winds and rain, was a favorite among soldiers, seafarers, and farmers. And there was Frey, a lascivious god of fertility, kinship, and peace who helped to ensure a bountiful harvest on land and sea. Frey possessed the most enviable of Viking equipment - a collapsible boat that could be folded up to fit into a small pouch when not in use and expanded to accommodate the entire company of the gods at Frey’s command.

These Viking gods had won their treasures of silver and gold by conquest and theft, by feats of daring and guile - just as did the mortal Vikings. In Scandinavian literature, the Viking god Thor is the essence of the hard-drinking, pugilistic Viking age. In one poem, he devours an ox, eight salmon, and three cups of mead (a wine made from honey) at a single meal. In others, he smashes enemy giants and demons by hurling boulders, thunderbolts, and his boomerang-like hammer into their enormous skulls.

By the early ninth century, some earnest Christian missionaries had begun to compete for heathen Viking souls by teaching them the Gospel.

Louis the Pious, the French king who reigned in France when the Vikings were beginning to settle there, periodically staged elaborate baptismal ceremonies to receive them into the Christian faith. The Vikings were willing enough to add yet another god to their pantheon, and many of them seem to have gone cheerfully through any number of Christian rituals for the prize to be had. On one occasion, there were so many Christian converts that there was not enough cloth for the long, white baptismal gowns that were traditionally given out on such occasions. So the fabric was cut into small pieces to make it go further. The oldest of the Vikings was then heard to complain loudly that this was the twentieth time he had been baptized, and he had always gotten a handsome gown out of it, but this sack they had issued to him was “fit only for a cowherd, and if I were not ashamed of being naked, you could immediately give it back to your Christ.”

In time, Christianity won some followers among the Vikings - but even then the Norsemen took to the new religion with ambivalence. Of Helgi the Lean, son of a Swedish sea rover and an Irish princess, it was noted “he believed in Christ and yet made vows to Thor for sea voyages and in tight corners and for everything that struck him as of real importance.”

Even to their own gods - who remained powerful long after the rise of Christianity in Scandinavia - the Vikings pledged their trust only on condition of mutual benefit. The saga of Hrafnkel illustrates how a Viking could rage when he felt betrayed by a god. Hrafnkel worshipped the god Frey. So solicitous was he of Frey that, when a harmless shepherd unwittingly made the mistake of riding a stallion that Hrafnkel had consecrated to the god, Hrafnkel killed the poor shepherd. But then, against all expectations, the lowly shepherd’s family succeeded in getting support from another wealthy landowner, who set out to avenge the slain shepherd. The landowner and the shepherd’s family caught Hrafnkel by surprise, stripped him of all his worldly possessions, and cast him out into the bleak land.

At that point, Hrafnkel angrily declared that he no longer would worship either Frey or the other gods if they could not take better care of him. Having decided to trust only to his wily, ruthless nature, he painfully won his way back to material prosperity and then opened a new cycle of violence by seeking a bloody revenge on his foes.

The Vikings loved such tales of fortitude and independence in the face of adversity. They roared with approval upon hearing of the old bondi who boasted: “At one time, the peace had lasted so long I was afraid I might come to die of old age within doors upon a bed.” They preferred to think of themselves in the image of such dashing figures as Gunnar Hamundarson, one of the heroes in the sagas, “a tall, powerful man” whose sword strokes “were so fast that he seemed to be brandishing three swords at once.” Gunnar had looks as well as talents, with his “fair skin and a straight nose slightly tilted at the tip, keen blue eyes, red cheeks, and fine head of thick flaxen hair.”

Another popular figure was Skarphedin Njalssan. One day, he caught sight of his hated rival Thrain Sigfusson standing with a throng of followers on an ice floe across a great gap of running water. Skarphedin made a gigantic leap over the water, holding his axe over his head, and came sliding along the ice so rapidly that Thrain was still putting on his helmet when down came the blow that split his skull open to his jaw, “spilling the back teeth onto the ice.” Jumping over a shield that was in his way, Skarphedin slid onto safety before any of his enemies could strike a blow at him.

Honor and daring, valor, strength and agility, all these were qualities the Vikings prized and upheld. There was another, somewhat less admirable side to their nature as warriors that the Vikings were only too pleased to highlight. This was their brutality toward their foes. Indeed, they seem to have exaggerated it deliberately in order to intimidate their enemies. Just as they carved the prows of their ships in the shape of dragons and other ferocious beasts to terrify the superstitious as they came surging out of the sea, so they cunningly circulated stories of their own savagery. One horrifying tale describes how, after a battle between Danish Vikings and two English kings in 867, the Norsemen broke open the rib cage of the captured King Ella of Northumbria and ripped his lungs out of his back - something they called carving the blood eagle, an allusion to the two lobes flapping like wings with the last dying breaths of the victim. Stories of such tortures, passed by the Vikings and the vanquished alike, conveyed the clear message to peoples everywhere that it would be wiser to yield than to try to thwart the relentless drive of the Norsemen.

Such cruelty was not the figment of a saga writer’s imagination; it occurred all too often. So did another kind of unruly behavior attributed to the Vikings, the bizarre actions with which some of them swarmed into battle. They would roll their eyes, bite the edge of their shields, and utter beastly howls. They would charge toward their adversaries without consideration of pain or danger and sometimes without any protective armor. A warrior who behaved this way was called a berserkr, an Old Norse word that has variously been interpreted as “bare skin,” meaning without a shirt, and “bearskin,” in possible reference to animal skins some of the men might have worn. Anglicized to berserk, the word came to symbolize the Viking terror. Not every Viking fought that way, of course. Some modern scholars suggest that such behavior may have been the result of drunken rages brought on by consuming huge drafts of ale or wine just before battle or of paranoia or perhaps of genetic flaws in individuals.

Whatever the cause, a number of Vikings - no one knows the percentage - did go berserk when they fought. And some kings and jarls found it useful to have bodyguards made up of these men or to use them as shock troops or simply to spread terror wherever they went.

With fighting occupying so much of their time at home and abroad, it would seem that the Norsemen lived by no laws at all. But such was not the case. Viking laws, like Viking literature, evolved out of age-old traditions. They were committed to memory, transmitted orally, and, when the occasion demanded, were recited aloud by a learned lawgiver.

Under Viking law, a jarl or bondi charged with a crime such as theft or murder was brought before a tribunal of judges made up of his peers. The accused could plead either guilty or innocent, and, if the latter, he could go on to argue his case by calling witnesses to testify both to the facts and to his honesty and good character. To further substantiate his case, he could seek - or the judges could require - trial by ordeal.

Such an ordeal usually began on a Wednesday, the day of Odin, god of wisdom. The person was given a handful of red-hot stones or scraps of metal to hold for a horrible minute or two, and then sent off with a bandage until Saturday, when the judges reconvened to look him over and reach a consensus. Their decision was based not on whether his hand was burned, which it invariably was, but rather on the severity and the cleanliness of the burn. If it was clean, the defendant was deemed to be innocent. If it was festering, he was pronounced guilty and given a sentence that ranged from a fine of money or goods to being banished.

A man found guilty of wounding one of his peers in a brawl was required to make “bone payment” to the victim in silver coins - one eyrir for a small wound, six for a large one - and to pay for the cost of treatment. “If a wound needs cauterizing,” the law stated, then the same eyrir “is payable every time cauterizing is necessary. But as physician’s fee, one eyrir is to be paid every month and two months’ worth of flour and two of butter. He who did the wounding must pay.”

Another law decreed a series of fines for improper touching of a woman: four ounces of silver for touching her wrist or her ankle, two and two-thirds ounces for touching her elbow. But a touch above the knee, the law went on, “is called the fool’s clasp; no money is payable for that - most women put up with it when it goes that far.”

There was certainly no humor to the other penalty to which miscreants might be condemned, and that was outlawry. A man found guilty of murder might be declared an outlaw, either for a limited period - a few months or a few years - or forever. As an outlaw, he could not fish, trade, join a Viking expedition, or seek help in an hour of need - not even from a member of his own family. Permanent outlawry was tantamount to banishment. Men on whom that lonely sentence fell had no choice but to flee. Outlawry was, in fact, the reason that many a Viking left his homeland.

As in most early societies, right went hand in hand with might, and enforcement of the laws depended, in large measure, on who was strongest, complainant or defendant. A king or powerful jarl might seek to uphold the laws as a matter of self-interest in order to strengthen his power. But where no such enforcement existed, a Viking might refuse to accept the judgment of a court or might refuse to appear altogether. In that case, the injured party - and his angered family - had no recourse but to seek restitution, if necessary in blood. And this was one of the primary reasons for the fighting and bloodshed that raged throughout the Viking age.

The question remains: Why the sudden burst of Viking energy at the end of the eighth century? Not the least impressive thing about their achievements is that there were so few of them. Scandinavia was not thickly populated. No more than 2 million souls could have been living there when the Viking age opened at the dawn of the ninth century. That was only a small fraction of the population of the empire that Charlemagne bequeathed to his son in 814.

One overriding reason for expansion overseas was that the Scandinavian population, although small in absolute terms, was growing rapidly - too rapidly to be peacefully absorbed into Norse society. Medieval ecclesiastics of other lands, observing this sudden explosion of Vikings out of the North, ascribed it to the sexual prowess of the northern heathen. They were polygamous, said Adam of Bremen, and had swarms of children. They had wild, promiscuous rites of spring every year, insisted the Norman chronicler Dudo of St. Quentin, and thus ensured an annual crop of babies.

A likelier explanation for the increase in population was a change in the climate. Northern Europe was perceptibly warmer around 800 A.D. than it had been in preceding centuries. The glaciers receded all over Scandinavia. There was more land that could be used for crops or pasture. The winters were shorter and milder. So significant a factor was winter in the life of northern countries that the Vikings counted time, not in years, but in winters.

A long cold winter would mean that the provisions put away in the fall might run out while the weather was still too harsh to replenish them by hunting or fishing. It also would mean that the weak, the old, and the young would die. Gentler winters meant that more babies would survive, more would grow up to swell the active, turbulent pool of younger sons who - since the property generally went to the oldest - were landless, foot-loose, bursting with energy, and ready for any adventure.

The mild winters also provided the Norsemen of the eighth and ninth centuries with an unusually protein-rich diet - their herds of cattle and flocks of sheep prospered, and more fish could be caught. This made the Vikings bigger and stronger, which gave them a significant advantage over their adversaries. European chroniclers tended to see them as Goliaths: “Never did I see a people so gigantic,” the Arab traveler Ahmad ibn Fadlan wrote. “They are tall as palm trees.” That wasn’t true, of course, but male skeletons in Scandinavian graveyards of the period average five feet eight inches, an impressive height for the time, when few people stood taller than five feet five.

The sagas had a more imaginative explanation for the Vikings’ advance on the world than diet and climate. Snorri Sturluson - the thirteenth century Icelander who set down a collection of sagas recounting the reigns of gods and kings from the beginning of time to his own day - ascribed the migration of the Vikings to the bloody deeds of Harald Fairhair, first known as Harald Halfdanson.

Around 860, he inherited a minor kingdom upon the death of his father and vowed not to groom his shaggy head until he had brought to heel a handful of jarls who contested his right to rule. The jarls did not submit meekly. One, named Herlaug, had himself buried alive in a funeral mound rather than submit to Harald. Those who seized their swords and summoned their retainers did so only to die on the battlefield. One by one, a number of others found resistance futile and followed the example of Herlaug’s brother Hrollaug, going on their knees to Harald. Then, the tale continues, the king called for his scissors and comb, had his long blonde locks cut off, and emerged from the barber as Harald Fairhair.

For all its fanciful detail, the spirited tale reflects the historical fact that sometime around 872 - almost a hundred years after the Lindisfarne raid - Harald Fairhair established the first centralized rule over the disparate settlements scattered throughout the hills and valleys of Norway, wresting from dozens of chieftains their lands and their time-honored independent authority over local provinces. In the near century that had elapsed since the plundering of Lindisfarne, the wide-ranging Viking ships had brought home more than booty from their expeditions abroad. Together with silver and gold came Christian fashions of cropped hair and centralized government.

The saga does not end there. It only begins. Some of the nobles - too proud to bow to Harald and loving life too much to resort to the funeral mound - found another way of evading Harald’s unwelcome aspirations. They loaded their ships with their wives, children, followers, cattle, slaves, and household goods and sailed across the sea and settled on new land. And, indeed, archeologists can date the arrival of Viking colonies on the Shetlands, the Orkneys, and Iceland to the last third of the ninth century - the exact moment when Harald Fairhair was consolidating his power as king of Norway.

Typical of the bondi who raided, invaded, and colonized abroad was one Egil Skallagrimsson, the tenth-century hero of a popular saga. His raiding expeditions were carried out pitilessly. The saga is a series of jubilant accounts of triumph over the weak and the gullible.

Egil was “exceeding ugly and like his father, black of hair,” says the saga. Notwithstanding that disclaimer, the eye of the Viking beheld him as a thing of beauty. He was a fearless fighter, a loyal friend, a colossal toper, who could empty one ox horn full of ale after another without passing out, and a daredevil who could keep his wits about him in the worst of predicaments.

Right from the beginning he showed promise. He learned to drink wine when he was three and committed manslaughter at seven. In a tiff over a ball game with a boy named Grim, “Egil became wroth and heaved up the bat and smote Grim,” killing his playmate, according to the saga. Servants and relatives came up with loud cries, and, before the altercation was over, seven men were dead. Egil’s mother, clearly the perfect helpmate for a Viking male, pronounced her son to be “of Viking stuff” and said that “as soon as he had age thereto,” the family should fit him out with “fleet keel and fair oars to fare abroad with Vikings” and “hew a man or twain.”

He was only twelve when the desire of his mother’s heart was granted. In due course, he was to be found leading Viking expeditions across the far seas. Coming ashore with a dozen followers in a region known as Kurland in modern Latvia, Egil scoured the countryside, slaying people at will and filling his ships with spectacular hauls of treasure. But an adventure would be no adventure at all without narrow escapes, and Egil had plenty of those.

In a clash one night with a Kurland farmer and a troop of followers, Egil and his comrades were overwhelmed by vastly superior numbers and taken prisoner. The farmer wanted to kill them all on the spot, but his son, a bloodthirsty lad, argued that it would be more pleasing to wait until morning when they could see the look on the faces of the men as they were being tortured. The farmer agreed, and the prisoners were fettered and thrown into an outbuilding while the Kurlanders went off to a victory feast.

Egil’s massive hulk had impressed his captors, and they had bound him hand and foot to a sturdy, upright post. But as soon as he and his friends were left unguarded, he used his strength to twist and tug at the pole until he was able to yank it out of the ground and work his way free from it. He untied the ropes on his hands with his teeth, and then he unshackled his feet and freed his companions. They began to explore the property. In another building, they heard cries from under their feet, pried loose some boards, and discovered three Danish Vikings who had been taken prisoner during a raiding expedition the year before and had been kept as slaves on the farm. With these new recruits to guide them, Egil and his men found their way to the Kurlanders’ treasure room and stripped it bare.

The men thought they had had enough adventure and profit for one day’s foray, but Egil objected that it was not warrior-like to slip away in the dark: “We have stolen the farmer’s property, and he does not know it. Let us return to the farmstead and tell people what has been going on.” The men ignored him and went back to their ship.

Egil returned alone. Coming upon a fire, he picked up one of the logs, carried it to the hall where the Kurlanders were carousing, and thrust it under the eaves of the roof. The roof caught fire, and boards began falling on the banquet table. As the building burned, most of the befuddled Kurlanders died where they sat. Those who tried to push their way out the door fell under Egil’s axe. When they were all dead, Egil marched back to the ship and claimed and got the lion’s share of the booty.

He then moved on, making additional and always profitable raids along the way on the coasts of Denmark, England, Holland, Norway, and Sweden. Finally, as the years passed, even Egil began to feel old and tired and returned to a farm in Iceland, where he took up the life of a wealthy bondi on his land.

He lived on to be a feeble, crippled, blind old man, huddling by the fire, ignored by his family, scolded by cooks and servant girls for getting in their way. But the Viking fires burned on in Egil to the end. He went out riding one day with two slaves and his chests of silver. He came back alone and never said a word of what had become of the slaves or the silver: Probably he had buried them all.

Later that year, Egil died and was buried with his weapons. Generations passed, and some outsized human bones were dug up and were widely believed to be Egil’s. The skull was remarkably large and heavy. It was set on a churchyard wall, and someone decided to test its hardness by swinging at it with the backside of an axe. “But the skull neither dented nor split,” relates the saga. “It only turned white, and from that anybody could guess that that skull would not have been easily injured by the blows of small fry when it still had skin and flesh on it.”

Such was the stuff of the Vikings.