In the photographs, the first thing that registers is the fear. Faces contorted into spasms, uncontrolled expressions, bodies fleeing, movement by instinct.
And always, somewhere in the background, a flash of light and a cloud of dust.
In the years since 9/11 similar photographs with similar fearful faces have emerged from across the world: from Afghanistan and Iraq, from London and Madrid. There were explosions and terror and fear and the deaths of innocent people before 9/11 as well, but what 9/11 did - its greatest legacy - was to create a matrix through which to understand this new world.
So much of what has come after has been seen as a reaction to that day's events, as if the burning of the towers wiped the slate of history clean. There was nothing before that led to 9/11, but much that followed.
In the weeks and months after 9/11, it became fashionable to talk about the terrorist attacks of that day as having "changed the world". This was overly dramatic. Huge swathes of the planet were barely touched by the day's events. Even much of the US continued as normal: people worked, studied and fell in love. But the years after have irrevocably changed some parts of the world, particularly South Asia and the Middle East.
There has also been an intellectual change, a change in the way of viewing and conceptualising the world. A matrix of belief that didn't exist pre-9/11 on anything like the same scale. Big events create their own intellectual ecology around them and 9/11 did just that.
The world is moved by accidents of history. In the aftermath of the attacks, the ideas of a handful of people had a disproportionate impact around the world because of their access to levers of power. In particular, an American political administration with a neoconservative view of the world was always likely to drag the US down a dangerous road and 9/11 offered the chance.
That day was a catalyst. In itself, 9/11 was a political event that America's leadership could have reacted to in various ways. The particular way politicians reacted to that event created a framework of ideas, one that has had a disproportionate impact across society. That framework was set by politicians, but because of the way other parts of the society reacted, the framework spawned intellectual trends.
To a very large extent, the framework was a reaction to the dark ideas that had led 19 men armed with boxcutters to board aircraft that morning. Al Qaeda believed it was fighting a war and identified the people of Islam in one camp and those of the West in another. Unpicked, it made little sense.
Yet the framework politicians, especially US politicians, accepted these premises almost without thought. It was a "war", they concluded, with the "West" in one corner, and a religion in the other.
In truth, there was no such distinction. There were many Muslims in the West and many westerners in Muslim countries. Even the concepts were flawed: the "West" was a political entity, Islam a faith community. In any case, Al Qaeda had no mandate to speak even for the people of Afghanistan, where its base was, let alone other Islamic countries or people.
Having accepted the premises of Al Qaeda, western politicians went on to create a narrative of danger and of difference, set around the faith of Islam. At first this was not a framework but gradually, by political positions and policies, an edifice was built up. By speaking of a "war" on terror, the narrative of danger was emphasised. By accepting there was an entity such as "Islam" that could move its followers in particular ways, the narrative of difference was set. And by talking - and thinking - in apocalyptic terms, by accepting 9/11 was an unprecedented event, the stage was set for an unprecedented response.
In significant part because of the reaction from politicians, 9/11 became more than an event. It filtered through society: policymakers and think-tanks found there was money on offer, from governments and private individuals, to conduct research within that framework.
Journalists uncovered stories within that framework, because there were column inches and airtime to be had.
The media played a significant role in following the political agenda, allowing itself to be swept along with political claims. Journalists went hunting for radical statements from any fringe Muslim organisation or mosque, framing it as a representative perspective. As the drumbeat to the Iraq war intensified, media outlets allowed themselves to buy into the threat, even allowing themselves to be fed information about weapons of mass destruction that, even at the time, made little sense.
But the themes - of security, of Islam, of difference and danger - were set by politicians. Together, they formed a matrix of ideas that sought to explain the world, to make sense of the events of those days and to chart at once an explanation and a map of how this new world fitted together.
Three themes can be discerned: in the West, the politics of fear; internationally, the clash of civilisations; and spiritually, the rise of the new atheism. Each was a direct reaction to 9/11. Each was rooted in the matrix of the politicians. And each turned out to be an intellectual dead-end.
Fear was the first thing people felt. The events of September 11 were a shock, not only because of the nature of the attacks themselves, but also because they occurred on US soil. For the US, 9/11 was a psychic shock. Americans had got used to the idea that their military might shielded them from harm. The planes punctured a hole in America's self-image that has still - a decade on - not been repaired. It was also a shock for the rest of the world. When a French newspaper declared, the following day, "We are all Americans now", it spoke of a sense that the certainties of the old world had been destroyed. It felt like the end of something.
The puncture created a vacuum that was soon filled by fear. Politicians fanned that fear for their own political ends, promising security that citizens understandably craved. Americans and Britons accepted preventive detention, profiling of Muslims and domestic surveillance. By giving up liberty, citizens hoped to regain their security.
The politics of fear worked, particularly in the US but also in Western Europe, at overriding the courts system for those held for suspected terror-related crimes. Instead of the civilian judicial process, suspects were subject to military detention and military trials - a further buy-in to the false "war" narrative.
In the name of security, the post-9/11 world has given up not only liberty, but also law. The drive to create a stable, international system governed by law - a project that had been ongoing since the Second World War - took a backseat to a relatively small security threat. There were huge changes in the international order, in particular the political contract that had governed international relations.
Chief among these was the idea that states that do not threaten others are not attacked. The doctrine of pre-emptive strikes, as outlined by the British and Americans, upended this. Iraq changed much, but one of its chief "lessons" for other countries was that the West might attack without provocation. Ironically, this reduced worldwide security as states such as Iran, Syria and North Korea became convinced that, without significant weaponry, they could not avoid being attacked.
When the US decided that there was an "axis of evil" comprising Iraq, Iran and North Korea, it begged the question of why it was willing to attack Iraq and threaten to attack Iran, but would only negotiate with North Korea, the only one of the three with a proven nuclear capability. The answer was not lost on America's opponents.
Elsewhere, international legal norms were flouted. The US - with shocking swiftness - gave up the Geneva conventions on the treatment of prisoners, spuriously declaring people it had picked up around the world to be "enemy combatants" and dumping them on an island where they had no rights. Euphemistic terms such as "extraordinary rendition" and "pain-based interrogation" were used for practices that were elsewhere known as kidnapping and torture.
The threat was real but politicians were unable to speak clearly about its reality. There were plots, serious attempts to puncture the security of some western countries, to attack the public transport networks. Some succeeded, with tragic results.
Yet politicians could not frame the threat properly for their audiences. They could not explain that the threat was real, serious and long-term, while also explaining that it was manageable and not all-consuming. They could not even speak the fear that many had: that these wars were making the threat worse.
This was not a new type of threat and it did not require a new way of life. Some could see this. An old, unused British poster from the Second World War started to appear on the streets and in the shops. It simply said: Keep calm and carry on. But its message was lost on leaders, ruling by fear.
In large part because of this politics of fear, an old theory resurfaced. Searching for a category within which to locate the threat, the politics of fear suggested the danger emanated from "Islam". This was a catch-all idea to encompass political disputes, immigration concerns and security threats across a vast area of the world.
According to the theory, the two civilisations of the "West" and "Islam" were fated to clash and 9/11 was one more skirmish in a long war. Days after 9/11, George W Bush, the US president, said "This crusade - this war on terrorism - is going to take a long time". Use of the word "crusade" seemed to entrench this idea of a civilisational clash.
In fact, it was a political clash. The theory - or, rather, the way the theory has been utilised in politics - is highly selective. A clash between Christian and Islamic civilisations would be almost too complex to contemplate. For one, the two are incredibly similar faith systems. Both revere the same God, the same prophets, have a similar conception of the good life, of heaven and hell and of the eschatology of the world. An alien civilisation cataloguing belief systems would rightly conclude these two were of one class and place them in a category called Abrahamic religions.
Moreover, neither the West, nor the East, nor Christianity or Islam can be hermeneutically sealed from each other, or from other civilisations. Each has made contributions to the other and many of the foundational texts of the West survived Europe's Middle Ages only because of their Arabic translations and interpretations.
In reality the Islamic world is vast, stretching from Indonesia, across Asia, throughout Africa, over the Arab world and Europe. The idea that such an enormous part of the world, with different cultures, languages, politics, all changing in different directions at the same time, could all be explained with reference to one religion is ludicrous. Further it is astonishing - and shows the enormous power of the matrix of ideas - that academics, journalists and writers had to spend so much time and effort to unpick what is, prima facie, ridiculous.
But the politics made the idea of a clash, by looking at these issues selectively. Vast swathes of the world and its lived experience were ignored. The Middle East became about the Israeli-Palestinian conflict, a conflict that has its religious warriors - Jewish settlers and Muslim militias - but is mainly about land and occupation. Immigration became about Muslim cultures integrating, rather than about poverty and opportunity. The complexities of local politics in Pakistan, military actions in Russia, cross-border tensions in Central Asia and competition for resources in the Middle East were all subsumed in a simplistic narrative of faith.
If Islam was the prism through which political conflicts were viewed, that triggered profound interest in both Islam and religion generally. Believing the matrix that had been imposed, politicians, theologians and other thinkers - Christians, Muslims and secular - began to ask what was it about Islam that made it uniquely dangerous.
Yet the question itself was nonsensical and one number told you why. There is not - and there has never been - a more widely believed God among the human race than the Abrahamic God. Fully half the planet has been taught such theology. If one part of that theology were so flawed, if it had within it messages of violence without end or reason, and yet had attracted billions of followers, it would unleash chaos across the planet. Nations would end because of this ideology, when in fact civilisations have risen.
Other thinkers began to look at the question more spiritually, concluding that the problem wasn't one particular religion, but religion generally. Of all the ideas that flourished in the post-9/11 framework, the new atheism was the latest (with the first book, The End of Faith, published in 2004) and the one most clearly identified with the political Left. At its heart, the new atheism argued that belief in God was unscientific and, therefore, unsustainable. Science was the cure for a superstition that had caused so much trouble in the world.
The "new atheism" grew out of a much longer-term intellectual trend, to do with the decline of authority in western societies (as represented by the church and organised politics). Richard Dawkins, the scientist who is one of the prime proponents of the new atheism, wrote: "I am not attacking any particular version of God or gods. I am attacking God, all gods, anything and everything supernatural."
But in its emergence and popularity in the post-9/11 climate, the new atheism was clearly capitalising on the climate of anti-Muslim suspicion, thus operating within the framework defined by politicians. Its arguments that faith misled people into violence were made against the background of the "war on terror". Not all of the authors associated with new atheism explicitly attacked Muslims, but they didn't need to: the background noise of news reporting showed its audience the dark side of religion.
The new atheism spoke especially to liberals, whose tendency to focus on complexity in public affairs was stymied by a simplistic anti-Islam narrative that could be applied in so many different areas. Liberals were under attack, trapped in a matrix of belief not of their making, each strand of which they disagreed with, but in a different way.
Liberals were against discrimination against Muslims, against the demonisation of a faith, against the erosion of civil liberties, against violations of international law, against attacking Iraq. Against, against, against. But not for. Liberals could not transcend the framework that had been imposed on them and ended up buying into the themes, embracing an argument that at least had some traction.
The new atheism had at its heart a fatal flaw: it had nearly nothing to say about the real world. New atheists did not want to deal with the complexity of faith, its many manifestations and its multi-faceted impact on the world. They could only wish it away, creating arguments that if only faith were removed from the hearts of men, all would be right with the world.
The trouble was, religion was everywhere. The US, the West's biggest country, was religious to its core. Across the Islamic world, faith was resurgent. In Africa and in parts of Asia, religion was rising. It was the secular world that was fading.
That was the problem with the new atheism. People supported it, read about it, watched television documentaries about it. But it had no way of talking to people about their lives or offering solutions. Those who were already believers, believed.
But it also had nothing to say to those liberals who genuinely believed more secularism was a good thing (apart from, "You are right, keep believing"). And it did not speak to the many millions in Europe, including the new Central and Eastern European countries, in the US and across the Arab world and Asia, who had varying degrees of faith, apart from telling them they were backwards and they should simply stop believing. One of the central political questions of our time, the proper role of faith in politics, was left unanswered and unanswerable by the new atheism.
In the end, the three themes -fear, the clash of civilisations, the new atheism - failed because they attempted to make sense of an attack they considered commensurately grand. But 9/11 was not the opening salvo in a great war for civilisation. It was not the first of a wave of warriors who would eventually establish a new caliphate. It was not a war that would be fought on battlegrounds worldwide. It was a meticulously planned operation, committed for political reasons, underpinned by religious fervour that required a measured, methodical response, using institutions and methods that already existed.
In the end, the intellectual ideas failed because they were looking for something new to explain what they thought was something new. But there was no grand narrative behind the attacks, no great idea that was born in those flames.
That bleak day in 2001 created a new face of terror. But this was not the face of the hijackers or their henchmen in remote cities. This was another face of the West, reflected in a mirror, angry, afraid and out for revenge. Contorted and uncontrolled, the political class couldn't see that the attacks would change the world only if they were granted that power. That is the clearest meaning of the past decade, a recognition and a curse. Nineteen hijackers in the skies above America didn't change the world of the West on a clear autumn day 10 years ago: it was the West that changed itself.
Faisal Al Yafai is a columnist for The National.