Bloodshed was foreseen by the people of Northumberland even before the Viking raiders came ashore on the Holy Island of Lindisfarne in AD 793.

An ancient manuscript recalls how ‘amazing sheets of lightning and whirlwinds and fiery dragons were seen flying in the sky’, but no omen could have prepared them for the barbarity that followed.

Leaping from their longboats, Viking invaders stormed the abbey and massacred priests, nuns and monks — even as they prayed at the altar.

‘They miserably ravaged and pillaged everything; they trod the holy things under their polluted feet, they plundered all the treasures of the church,’ claimed one chronicler of the time.

‘Some of the brethren they slew, some they carried off with them in chains…’

In the monastery on neighbouring Iona, one defiant abbot was ‘cut in pieces with severed limbs’. But even then his assailant was not satisfied, hacking at his entrails in a frenzy of blood-lust.

Viking invaders stormed the abbey and massacred priests, nuns and monks — even as they prayed at the altar

So began a reign of terror that saw the Vikings slaughter their way across England, Scotland and Ireland — as well as large swathes of North-West Europe — for more than a century.

With names like Erik Bloodaxe and Thorfinn the Skull-Splitter, these warlords showed no mercy — which makes it all the more peculiar that recent historians seem determined to paint them in a rather different light.

While not quite suggesting that they should be renamed Erik the Ever-so-Polite and Thorfinn the Touchy-Feely, research published this week suggests we should take a more nuanced view of Viking marauding.

The report in the journal Nature involved genetic analysis of more than 400 Viking skeletons from burial sites across Europe. Among the most striking findings is that Scandinavian Vikings inherited genes from both Southern Europe and Asia so, far from being the blonde brutes we imagine, they were as likely to have had brown hair.

Fascinating stuff, but more controversial are the conclusions we are expected to draw from the bodies of two males buried in Orkney. While their grave contained swords and other Viking artefacts, these men were actually Picts — Celtic-speaking people who lived in Scotland at the time of the invasions. And yet they appear to have been respected as Vikings.

According to the study’s lead author Dr Daniel Lawson of the University of Bristol, this suggests ‘a different side of the cultural relationship from Viking raiding and pillaging’.

The implication is that far from being the murderous types we imagine, the Vikings mixed willingly with other cultures who accepted their way of life. But as the Vikings’ own accounts make clear, anyone who did collaborate with them was likely forced into doing so rather than persuaded.

 ‘Great numbers of English flee before our swords,’ boasted one Viking poem.

Forewarned of a raid, the men and women of Fife were said to have ‘dragged themselves off to the woods and wastes with weeping and wailing’. On return they would have faced famine as the Vikings would have smashed their farm tools before plundering and torching their granaries.

Women were raped and prisoners were sold into slavery, often into Asia and the Middle East where the preference for eunuchs saw them castrated upon capture.

Vikings had names like  Erik Bloodaxe and Thorfinn the Skull-Splitter and terrorised across England, Scotland and Ireland for more than a century

But even those poor souls might have been considered lucky not to have been dispatched straight away — for the Viking cult of the warrior valued killing for its own sake. Doing so quickly and efficiently was an art learned from childhood by the sons of noblemen and their weapon of choice was the sword — often handed down from father to son and given such telling names as ‘Brainbiter’.

Apprentice combatants learned how to twist and turn wearing heavy mail tunics and iron helmets, and to wield swords, spears and axes while protecting themselves with shields.

The training for hand-to-hand combat required great stamina and strength and warriors were taught to disable their foes by slicing into the thigh or arm before delivering the fatal strike to the head — with such force the skeletons of their victims reveal blows that smashed through helmets and skulls to pulverise the brain.

Among the Viking ranks were ‘berserkers’ (Norse for ‘bear-like’), legendary warriors who are believed to have gone into battle without armour, protected merely by the rage they worked themselves into.

One troop on the eve of battle were described as ‘mad as dogs’. Others donned the skins of wolves, somehow imagining they could absorb their ferocity as they ‘bear bloodstained swords to battle’.

Intimidation was just one psychological tactic deployed by the Vikings. Another was the element of surprise — these accomplished shipwrights and navigators could launch their amphibious assaults in tides and weather conditions that were daunting to their enemies.

Their longboats were described by one Viking poet as ‘wave stallions’ and they painted ravens on the sails, joking grimly that these flesh-devouring birds were brothers-in-arms who followed them into combat to feast on the dead.

The raids were triggered by overpopulation and food shortages in their Scandinavian homelands, and the knowledge that Britain and Ireland had inadequate defences. But although the treasures in churches and monasteries could be easily plundered, still the Vikings fought among themselves when dividing the spoils.

The losers in these feuds suffered ritual and unimaginably cruel deaths. Torf-Einar, the one-eyed Viking ruler of Orkney, ordered his men to carve the outline of an eagle on a prisoner’s back, slice the ribs from the backbone and then pull out the man’s lungs as an offering to the god, Odin.

For Vikings, killing quickly and efficiently was a form of art, that had to be taught since childhood

Such appalling, ritualised deaths were also meted out to Anglo-Saxon leaders as the Vikings colonised land from Scotland to East Anglia — an area that became known as Danelaw. Being a superstitious people who understood the concept of an afterlife, they were impressed by the Christian beliefs of those they conquered.

Viking rulers such as King Olaf Tryggvason of Norway realised the advantage of embracing a religion which suggested that those who followed their monarch were also following the will of God. However, the Viking version of Christianity was characteristically violent.

‘It is my will that you shall be baptised and all the folk that serve you,’ Tryggvason informed Earl Sigurd of Orkney. ‘Else you shall die here at once, and I will ravage all the isles with fire and sword.’

Only in 10th-century England did they meet their match, losing to Anglo-Saxon king Alfred the Great, whose peasant army fought alongside professional soldiers — proving the Vikings were not invincible.

Finally defeated, they were allowed to settle in Danelaw as subjects of Alfred and his descendants — bu the Vikings had not done with thoughts of conquest yet.

In 1066, Harald Hardrada, the last great Viking leader, was defeated in

his attempts to conquer England. Killed at the Battle of Stamford Bridge, he left the English throne to be fought over by the Anglo-Saxon King Harold, and William, leader of the Normans — descendants of the Vikings who had settled in northern France. Clearly the Viking warrior spirit lived on in William the Conquerer and his men, combined with the latest continental combat techniques.

Armed with deadly lances, Norman knights fought on horseback, charging through their opponents hacking at them from above, backed by missiles from bows and crossbows.

As history records, William was ultimately the victor at the Battle of Hastings but, although Harold was killed there, it has been suggested he is not the warrior pulling an arrow from his eye as famously shown in the Bayeux tapestry. Some historians believe that his death came instead from a blow to his thigh from a mounted Norman swordsman, delivered with such force that archaeologists believe it would have driven through the chainmail to his flesh and bone.

Either way, it was a killing of which William’s Viking ancestors would no doubt have been proud. Their hair colour may not have been what we’ve long imagined but, whether brown-haired or blond, there is no question their colourful combat skills made them unbelievably brutal warriors.

When al-Qaeda destroyed the Twin Towers almost exactly 19 years ago, the aims of the terrorists were not fully understood by many in the western media. Osama bin Laden intended not just to wage war against the non-Muslim world but to present himself — and his jihadi narrative — as the new voice of Islam. He was fighting a war of ideas, as well as one of terror. One of the best ways to understand and combat the ideological side of the jihadi movement is to read the works of the philosopher Bassam Tibi, who has been fighting fundamentalist ideas for the past four decades.

His work — speeches, essays and more than 40 books — tracks the methods by which Islamists operate. With forensic precision, he details the ways in which they are inimical to most of Islam’s history. ‘To protect themselves against criticism,’ he once wrote, ‘Islamists invented the formula of “Islamophobia” to defame their critics.’ The word ‘serves as a weapon against all who do not embrace Islamist propaganda, including liberal Muslims’.

I’ve been an admirer of his work for years and flew to Frankfurt to meet him and to hear his story first-hand. He grew up in Damascus and became hafiz (someone who has memorised the Quran) at the age of six. There was a clash of civilisations in his head. ‘My family was against colonialism, against imperialism, against the hegemony of the West — but we were still admirers of the West,’ he says. ‘We would go to the Quranic school, then after Friday prayers go to a party with kids and dance rock ’n’ roll. The culture we looked up to was American.’ He had his eye on Harvard but his father — a property magnate whose company had built half of the new buildings in Beirut — was keen on Germany because it had sided with the Arabs in the first world war. So Tibi went to Hamburg in 1962 and never came back.

‘I came to Germany as an anti-Semite,’ he admits. ‘We were educated that way. I used to fight with my brother who was two years younger. My mother — who was not an anti-Semite but this is just the language we used then — said to me in Arabic: “Leave him. You can do this to a Jew but not to your brother.” Then I met two Jews and they changed my life.’

They were the philosophers Theodor Adorno and Max Horkheimer, the founders of the Frankfurt School of critical thinking. They had fled Nazi Germany for America and only returned after the second world war. They wanted to find out why, after the Enlightenment, with all of its logic and beauty, humanity in the 20th century had started ‘sinking into a new kind of barbarism’.

Tibi had similar questions about Islam and Islamism. Ernst Bloch (a third Jew) anchored Tibi’s thinking in Islamic rationalism. Bloch wrote about Ibn Sina — born in the Samanid Empire in around 980, the golden age of Muslim civilisation — who had plenty to say about human equality and the intertwining of Arabic and western thought.

‘Bloch says the Enlightenment started in medieval Islam,’ Tibi tells me. Tibi makes an important distinction between mufti Islam, the world of the fatwa-givers (a type of Islam that’s on the rise in Britain too), and the world of Enlightenment Islam, highlighted by Bloch. The mufti world of Islam is ‘leading Muslims backwards’, Tibi says. He seeks to explain, revive and promote the Islam of early Enlightenment — the ‘Islam of Light’.

I ask him when he first noticed that something was going wrong in the Muslim world. ‘It started with the Six Day War,’ he says. Israel’s victory was a massive humiliation for the secular Arab regimes in the eyes of their citizens, especially when Israel gained the Gaza Strip and the Sinai Peninsula from Egypt. At the time, Tibi hoped that the response to this would be a new Arab Enlightenment. Instead, religious extremists rose to positions of power. His first physical confrontation with them came in 1979 when he presented an academic paper in Cairo and was denounced as a heretic.

He has long thought it interesting that Arabs constitute only a fifth of the world’s Muslims, yet seem to direct most modern Muslim thought. ‘If you want to know where Islam is going,’ he says, ‘you don’t go to Turkey. You go to Egypt.’ His early work on Cairo’s political institutions drew him to the attention of the political scientist Samuel P. Huntington, who went on to acquire worldwide fame with his 1993 essay ‘The Clash of Civilizations’, in which he argued that faith (especially Islam) would be the world’s next battle line.

It’s an argument that Tibi had tried to talk him out of long before. ‘I was trying to correct his knowledge about Islam. It’s a conflict, I said, not a clash. Dealing with Huntington was like dealing with an Islamist: it’s all about language. If you “clash”, it’s over. But in a conflict, there is a conflict resolution. We can negotiate, we can talk. We say: “There is a western Islamic conflict, and there are ways to deal with it.” But a “clash”? The word is essentialised. It’s saying that we Muslims are backward people.’

Tibi is also an expert in sharia law, which is often deployed by fundamentalist states in the name of being true to Islam. But Tibi argues that it is not fundamental to the religion. ‘If God believed what the Islamists believe, the term “sharia” would occur every second or third page in the Quran. But it is mentioned only once. And not in the meaning of law, but in the meaning of morality or guidance. The Quran was revealed in the 7th century. The sharia schools in Sunni Islam were created in the 8th century, 100 years later.’ The use of sharia in the modern political and confrontational sense, he says, started with the Muslim Brotherhood in Egypt in the 20th century.

Tibi argues that the Islamist agenda is far more modern than the fundamentalists want to admit, and springs from the political totalitarianism invented in the last century. Taking Hannah Arendt’s definition of the term, he categorises all aspects of this ‘political religion’ as authoritarian. He draws out the modern, totalitarian nature of Islamism in his research: for example in his analysis of the works of Hassan al-Banna, who founded Egypt’s Muslim Brotherhood in 1928. It was this movement, Tibi says, that came up with the idea of modern-day jihadism and enforced the notion of Islam being incompatible with western values.

‘When I sit with civilised Europeans, they look at me. I am a Muslim, I am a democrat: what do they think is wrong with me? What do they dislike about me being a Muslim? They say, “But you are more European than a Muslim.” I say no. That’s why I coined the term Euro Islam, European Islam.’

Using the language of medieval Muslim rationalists from Farabi to Ibn Rushd, famous in the Latin West as Averroes, Tibi defines Islam of the Enlightenment as advocating the primacy of reason. He also takes a definition of Enlightenment from Kant: that reason is the court in front of which every-thing must establish itself. But Ibn Rushd made this point in the 12th century, he says. ‘So why are we Muslims now dismissed as underdeveloped people when our greatest philosopher, Ibn Rushd, foresaw things six centuries ahead of the greatest philosopher of Europe?’ In fact, he says, Ibn Rushd perhaps has more relevance to our age, ‘the age of the return of religion’, because his work focused on the unity of faith and reason.

This certainly is the battleground now. The much-needed reformation of Islam will not be about headscarves and beards. Terrorism will only end when scripture is not taken literally. In pursuit of such an enlightened future, Tibi’s work can remind westerners — and Muslims — of a different, less divergent history.