What really happened

Battle of Edington, May 878. In January 878 Guthrum's surprise attack on Chippenham drove King Alfred into the Somerset marshes at Athelney. Wessex was the last English kingdom still unconquered. In May Alfred gathered the men of Somerset, Wiltshire and Hampshire, defeated Guthrum at Edington and besieged him for two weeks. Guthrum accepted baptism and withdrew to East Anglia.

What historians say

Historians generally agree that Wessex came close to collapse in the first months of 878 and that Alfred's survival mattered: the other English kingdoms had already fallen or been divided. They also caution that Viking armies were coalitions that tended to break up and settle, and that Scandinavian rulers in England quickly adopted Christianity and local methods of government. A Danish Wessex would have changed the dynasty and the map more surely than the underlying culture.

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The change

Alfred's hastily assembled army breaks at Edington, or the king is killed in the fighting, and Guthrum remains master of Wessex.

What might have followed

• Wessex would probably have been partitioned or handed to a compliant client king, as Mercia had been in 874.
• The fortified burhs, the reformed army and the fleet that Alfred built after 878 might never have existed, leaving no base for a later English reconquest.
• A single kingdom of England might have formed much later, or under a Scandinavian dynasty ruling from York or Winchester.
• English would probably contain even more Norse vocabulary, and the Old English translations and chronicle sponsored by Alfred's court might never have been written.
• The settlers would still very likely have accepted Christianity and blended with the local population within a few generations, as they did in East Anglia and Northumbria.

What really happened

Siege of Paris (885–886), November 885 – October 886. A very large Viking fleet demanded passage up the Seine past the fortified bridges of Paris. Count Odo and Bishop Gozlin refused and held the island city for almost a year with a small garrison. Emperor Charles the Fat finally arrived, but instead of fighting he paid 700 pounds of silver and let the Vikings go on to plunder Burgundy.

What historians say

The defence of Paris is usually treated as a turning point less for military reasons than for political ones: it discredited Charles the Fat and made the reputation of Odo's family. Historians also point out that Paris had been taken or ransomed before, in 845 and again in the 850s and 860s, without lasting conquest, because the raiders wanted plunder and passage upriver rather than the city itself. A fall in 886 would most plausibly have changed dynasties, not populations.

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The change

The bridge towers fall during the first assaults in the winter of 885–886 and the Vikings take the city before any relief army can arrive.

What might have followed

• Count Odo would probably not have won the prestige that carried him to the West Frankish throne in 888, the first king from the family later known as the Capetians.
• Paris, then a modest island town, might not have gained the reputation that helped make it the centre of the French kingdom.
• The Seine valley would have lain open, and a permanent Scandinavian lordship on the river might have appeared a generation before Normandy.
• Charles the Fat's authority, already weak, would probably have collapsed even sooner than it did in 887.

What really happened

Treaty of Saint-Clair-sur-Epte, Autumn 911. After Rollo's Vikings were beaten outside Chartres in July 911, King Charles the Simple nevertheless came to terms: Rollo received land around Rouen on the lower Seine in return for baptism, loyalty and defending the river against other raiders. No text survives; the story comes mainly from Dudo of Saint-Quentin, a century later.

What historians say

Scholars stress that the grant was not unprecedented: Frankish rulers had already ceded land to Viking leaders in Frisia and elsewhere, and those arrangements faded. What was unusual about Rouen is that it lasted, thanks largely to Rollo's successors. Many historians also think the agreement recognised a fact, since Northmen already controlled the lower Seine. A flat refusal would therefore have been hard to enforce, which makes the complete absence of any Norman settlement a less likely outcome.

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The change

Encouraged by the victory at Chartres, Charles refuses to cede any territory and tries to drive the Seine Vikings out by force.

What might have followed

• Without a recognised Norse principality at Rouen there would probably have been no Duchy of Normandy and no Norman conquest of England in 1066.
• England would most likely have stayed in the Anglo-Scandinavian world, and English would have absorbed far fewer French words.
• The Norman states in southern Italy and Sicily, and the Norman part in the early crusades, might never have come about.
• The Seine Vikings would probably have gone on raiding, or been settled later on different terms, since Frankish rulers had no means of removing them.

What really happened

Christianization of Kievan Rus', c. 988. The Primary Chronicle says Prince Vladimir of Kyiv weighed Islam, Judaism, Latin Christianity and Greek Orthodoxy, and that his envoys were overwhelmed by the liturgy in Hagia Sophia. In practice the choice followed an alliance: Vladimir sent warriors to Emperor Basil II, married the emperor's sister Anna, was baptised around 988 and had the people of Kyiv baptised in the Dnieper.

What historians say

Most historians read the chronicle's 'testing of the faiths' as a literary set piece rather than a report. The real decision was shaped by the Dnieper trade with Constantinople, by Christians already living in Kyiv, by Olga's own baptism, and by the military and marriage alliance of the 980s. Latin Christianity was a genuine alternative, as the failed German mission of 961 shows; Islam was the least likely. The mainstream view is that Orthodoxy was much the most probable outcome.

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The change

Vladimir accepts baptism from Latin missionaries, as his grandmother Olga had once requested from Otto I, or adopts the Islam of his Volga Bulgar trading partners.

What might have followed

• A Latin Rus' would probably have developed alongside Poland and Hungary, using the Latin alphabet and looking to Rome rather than Constantinople.
• The Orthodox world would have been far smaller, and the later idea of Moscow as heir to Byzantium could hardly have arisen.
• A Muslim Rus' would have tied the Dnieper and Volga routes more closely to the Islamic world and moved Europe's religious frontier far to the west.
• Church Slavonic literature and the Cyrillic script might have remained a mainly Balkan tradition.

What really happened

Battle of Clontarf, 23 April 1014. On Good Friday 1014 the army of the high king Brian Boru fought the king of Leinster, the Norse of Dublin and Viking allies from Orkney and Mann. The battle lasted all day. Brian's side won, but Brian himself, his son Murchad and his grandson were killed, and Sigtrygg Silkbeard went on ruling Dublin until 1036.

What historians say

Modern historians see Clontarf less as Irish against Vikings than as a revolt by Leinster and Dublin against the overlordship of Brian's Munster, with Scandinavians hired as allies. Norse military power in Ireland had already been checked at Tara in 980 and Glenmama in 999. The heroic version comes largely from Cogadh Gáedhel re Gallaibh, a 12th-century work written to glorify Brian's descendants. The battle was close, but a different result would probably have changed less than legend suggests.

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The change

The Leinster and Norse army holds the field at the end of the day, and Earl Sigurd of Orkney survives the battle.

What might have followed

• Brian's attempt to make the high kingship a lasting monarchy for his own family would have ended — as, in the event, it largely did with his death.
• Dublin would have remained a self-governing Norse-Irish trading town under Sigtrygg, much as it actually did.
• The earls of Orkney might have gained a foothold in Ireland, extending their sea-lordship across the Irish Sea for a time.
• The later image of Brian as the king who drove out the Vikings would not exist, and Irish national memory would have a different founding hero.

What really happened

Break-up of the North Sea Empire, 12 November 1035 – 8 June 1042. Cnut ruled England, Denmark and Norway together. When he died at Shaftesbury in 1035, Norway had already chosen Magnus the Good, Harthacnut was pinned down in Denmark and Harold Harefoot took England. Harthacnut reunited England and Denmark in 1040 but died suddenly at a wedding feast in 1042, childless and in his early twenties.

What historians say

Historians usually describe Cnut's empire as a personal union held together by one exceptionally able ruler, with no shared institutions, law or administration. Norway had broken away before he died. Most therefore doubt that the whole could have lasted long, even under a capable heir. A continuing link between England and Denmark is considered more realistic: it had worked from 1016 to 1035 and briefly again from 1040, and Danish kings were still claiming England in the 1080s.

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The change

Harthacnut does not die in 1042 but reigns for decades over England and Denmark and leaves an adult heir.

What might have followed

• England would probably have remained tied to Scandinavia rather than to northern France for at least another generation.
• Edward the Confessor might never have reigned, removing the kinship and promises on which William of Normandy later based his claim.
• The crises of 1066 would not have happened in the form we know, although Norwegian kings would probably still have contested the inheritance.
• A king ruling both sides of the North Sea would have had to govern largely through powerful earls, and that could have produced a different kind of break-up later.

What really happened

Battle of Stamford Bridge, 25 September 1066. Harald Hardrada of Norway and Tostig landed with about 300 ships, beat the northern earls at Fulford and received York's submission. Harold Godwinson marched north in four days and caught them unprepared at Stamford Bridge. Hardrada and Tostig were killed; the chronicle says only 24 ships were needed to carry the survivors home. William landed in Sussex three days later.

What historians say

Historians agree that surprise decided Stamford Bridge: part of the Norwegian army was away with the ships and, according to later saga tradition, many men had left their mail behind. The result was therefore far from inevitable. They are more sceptical that Hardrada could have held the whole of England afterwards, with William's fleet waiting across the Channel and southern England hostile, although the north had strong Scandinavian ties and had just submitted to him.

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The change

The Norwegians get warning of Harold's approach, fight fully armed and with their whole army, and Harold Godwinson is the king who falls.

What might have followed

• England's future would then probably have been decided between two invaders, Harald of Norway and William of Normandy, rather than by an English king.
• Hardrada would most likely have built his power on the Anglo-Scandinavian north around York, and the kingdom might have been divided for a time.
• Had he gone on to defeat William as well, England would probably have stayed in the Scandinavian orbit, as it had under Cnut.
• Hardrada was about fifty and his sons were young, so a Norwegian regime in England would have been fragile once he died.

What really happened

Battle of Hastings, 14 October 1066. The battle lasted from about nine in the morning until dusk, unusually long for the period. The English shield wall on its ridge held against archers, infantry and cavalry for hours, and at one point a rumour spread that William was dead. Feigned retreats thinned the English line, and Harold was killed late in the day.

What historians say

Hastings is widely regarded as one of the most evenly balanced decisive battles of the Middle Ages. The surviving accounts agree that it lasted all day and that the Norman army nearly broke at least once. Harold did not need to destroy William, only to avoid defeat, and many historians think he might have done so with a more rested army or a few more days to gather men. Few battles of such consequence are considered to have been so open.

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The change

The shield wall holds until nightfall and Harold survives; William, with the sea at his back, cannot break through.

What might have followed

• William would probably have had to withdraw or been destroyed, since he had no secure base and little prospect of reinforcement so late in the year.
• England would have kept its Old English aristocracy, bishops and land law instead of seeing them replaced within a generation.
• English would probably have far fewer French and Latin loanwords and might look closer to Dutch or Frisian today.
• English kings would not have held great lands in France, removing a root cause of centuries of Anglo-French warfare.
• England would have remained exposed to Scandinavian claims, such as the Danish invasion that actually came in 1069.

What really happened

Norse settlement at L'Anse aux Meadows, c. 1000–1021. The sagas describe several expeditions from Greenland to Vinland, the largest led by Thorfinn Karlsefni with settlers and livestock, all abandoned within a few years after clashes with the local inhabitants. Archaeology confirms a Norse base at L'Anse aux Meadows in Newfoundland, with eight buildings, used only briefly; wood there was cut in 1021.

What historians say

The mainstream view is that Vinland failed for structural reasons. Greenland itself held only a few thousand people at most, the voyage was long and dangerous, the Norse had no real military advantage over far more numerous local populations, and Vinland offered little that could not be had from Europe except timber. Greenlanders did keep sailing west, probably for wood: an Icelandic annal records a ship that had been to Markland in 1347. A lasting colony is generally judged unlikely.

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The change

The Greenlanders commit more people, establish peaceful trade with their neighbours, and a farming settlement takes root on the Gulf of St Lawrence.

What might have followed

• Regular sailings would probably have made the western lands common knowledge in Icelandic and Norwegian ports centuries before 1492.
• Iron tools, livestock and Old World diseases might have reached Indigenous peoples of the north-east much earlier and on a smaller scale, with effects that are very hard to predict.
• Greenland, with timber and a trading partner close at hand, might have had a better chance of surviving the 15th century.
• The colony would still have been tiny and remote, and would most likely have been absorbed by its neighbours or abandoned eventually.

What really happened

End of the Norse settlements in Greenland, c. 1350–1450. Founded around 985, the two Norse settlements in Greenland held a few thousand people at their height. The Western Settlement was deserted by the mid-14th century. The last written record is a wedding at Hvalsey church in 1408, and the Eastern Settlement died out later in the 15th century. Climate, trade, isolation and competition are all debated causes.

What historians say

Research has overturned the older picture of farmers who refused to change. Isotope studies of skeletons show that the Greenlanders ate more and more seal, until marine food dominated their diet. Scholars now stress the collapse of the walrus-ivory trade, a cooling and stormier climate, fewer ships from Norway and steady emigration, more than any single catastrophe. With so small a population, survival was never secure, but a remnant holding on is not thought impossible.

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The change

The Greenlanders go further in adopting the hunting technology of their Inuit neighbours and keep at least an occasional shipping link with Iceland or Norway.

What might have followed

• A small Norse-speaking Christian community might still have been living in the southern fjords when the missionary Hans Egede arrived in 1721 expecting to find one.
• A distinct Greenlandic Norse language, a sister of Icelandic and Faroese, might exist today.
• There would probably have been much more contact, trade and intermarriage between Norse and Inuit Greenlanders.
• The Danish-Norwegian crown's claim to Greenland would have rested on continuous settlement instead of a medieval memory.

What really happened

Christianization of Scandinavia, c. 965–1100. Harald Bluetooth of Denmark was baptised around 965 and proclaimed it on the Jelling stone. Norway followed under Olaf Tryggvason and Olaf Haraldsson, Iceland by a decision of the Althing around 1000, and Sweden more slowly during the 11th century. By 1164 all three kingdoms had their own archbishops, at Lund, Nidaros and Uppsala.

What historians say

Historians see the conversion as driven from the top. Kings and chieftains found in Christianity a source of prestige, allies, administrators and royal ideology; Anders Winroth's 'The Conversion of Scandinavia' (2012) argues this case in detail. Trade with Christian Europe pulled the same way. A long refusal is therefore considered improbable, though not unthinkable: Lithuania remained officially pagan until 1387, at the price of two centuries of crusading warfare.

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The change

The Scandinavian kings of the 10th and 11th centuries refuse baptism and instead organise the old cults into an institution of their own.

What might have followed

• Pagan kingdoms on the edge of Latin Europe would probably have become targets of crusades, as the Wends, Prussians and Lithuanians later were.
• Their kings would have lacked the literate clergy, written law and diplomatic recognition that helped Christian rulers to build stable monarchies.
• Raiding might have continued longer, since Christian and pagan rulers regarded each other as legitimate prey.
• Paradoxically, less Norse mythology might survive, because it was Christian Icelanders writing in the Latin alphabet who recorded it.

What really happened

Battle of Largs and the Treaty of Perth, 2 October 1263 – 2 July 1266. In 1263 King Haakon IV sailed with a great fleet to defend Norwegian rule in the Hebrides and Mann. Autumn storms drove ships ashore at Largs, the fighting was indecisive, and Haakon died in Orkney that winter. In 1266 his son ceded the Hebrides and Mann to Scotland for 4,000 marks and an annuity. Orkney and Shetland followed in 1468–72.

What historians say

Historians generally regard Norway's hold on the Hebrides as loose, expensive and hard to defend at such a distance, while Scottish royal power in the west was growing steadily; the Treaty of Perth acknowledged that balance. Orkney and Shetland are a different matter. The pledge of 1468–69 was meant to be redeemable, and Danish kings tried several times in later centuries to buy the islands back, without success. Keeping the northern isles is thought more plausible than keeping the west.

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The change

Haakon's fleet arrives in high summer and forces Alexander III to recognise Norwegian sovereignty; two centuries later the royal dowry is paid in cash and the northern islands are never pledged.

What might have followed

• Scotland's western and northern islands might today resemble the Faroes: self-governing Nordic communities under a Scandinavian crown.
• Norn, the Norse language of Orkney and Shetland that died out by the 19th century, might still be spoken.
• Scottish kings would probably have faced a rival sea power on two coasts, and the Gaelic-Norse lords of the Isles might have played one crown against the other for longer.
• The seabed around Shetland and Orkney, with its oil and gas, would probably lie in Scandinavian rather than British waters.

What really happened

Battle of Dyrrhachium, 18 October 1081. Robert Guiscard, the Norman duke of Apulia and Calabria, crossed the Adriatic in 1081 and defeated Emperor Alexios I Komnenos at Dyrrhachium, where the Varangian Guard was cut to pieces. But revolt in Italy and a German march on Rome, both encouraged by Byzantine gold, called him home. His son Bohemond was checked in Thessaly, and Robert died of fever in 1085.

What historians say

Anna Komnene's Alexiad presents Robert as aiming at the imperial throne itself, and Alexios's position in 1081–83 was truly precarious. Modern historians are divided on how far Robert's ambitions went and are cautious about his chances. Constantinople's walls had defeated every besieger for centuries, and the Normans had been beaten at sea by the Venetians. Conquering part of the Balkans is considered possible; taking and holding the capital is generally thought to have been beyond his means.

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The change

No crisis recalls Robert to Italy in 1082, and he marches east along the Via Egnatia while Alexios has neither an army nor money.

What might have followed

• A Norman dynasty might have ruled in Constantinople more than a century before the crusaders who actually seized the city in 1204.
• Alexios would not have been emperor to appeal for western help in 1095, so the First Crusade might have taken a very different form or not happened as it did.
• A Latin ruler would probably have faced resistance from the Greek church and population, and the Seljuk Turks already held most of Anatolia.
• Venice, which won sweeping trade privileges in 1082 as the price of helping Alexios, might not have gained its commanding position in the eastern Mediterranean.