One of the people associated with this early story is Alexander the Great. What do we know about his role in exploring Asia?

In the fourth century BC, his armies made it all the way into north-west India. Precisely what happened next is hard to know for sure, because there was so much romanticising about what he did. At that point people believed that India was the furthest east you could go before you got to what they thought of as a great river which flowed all around the edge of the world. When Alexander got there, though, it seemed that he and his armies realised that India was much bigger than they were expecting, and that the opposition was more serious. We think they encountered war elephants, for instance, and their size, sound and smell must have been terrifying.

For whatever reason, Alexander’s armies turned back. But one of the things I think that stayed with them – and it’s a theme that runs throughout my book – is the sense of India not just as a place of strangeness and of wealth, but also of spiritual depths. One of the things we know about Alexander is that he had a great entourage with him that included philosophers as well as warriors. As they travelled, they met Indian holy men who got into conversation with Alexander about the big questions of life and death. We don’t know if this is true or not, but they also apparently chided Alexander for his warmaking, asking him, “Now you’ve seized all this territory and wealth, where are you going to take it?” So this idea of the east as a place of wisdom and philosophical questioning goes all the way back to Alexander the Great.

And were these three threads – wisdom, wealth and strangeness – the factors that pulled people from the west to Asia into the early part of the medieval period?

I think so, yes. And that wealth took many forms. Emeralds and sapphires were said to flow through the rivers of India, for instance, and that land was supposedly also home to gold-digging ants bigger than foxes that would dig up the sand and the gold dust within it. There was a fantasy of India being quite wealthy. But as well as the fantasies, there were also real commodities such as spices, which people in Europe had been big fans of all the way back to the days of the Roman empire. They had become part of the culture of medieval Europe, used for everything from cuisine and medicine to religious ceremonies. So Asia was really important by this point.

And some people, depending on how they read Genesis in the Bible, also expected there to be a paradise located in the east – some people wondered whether those spices grew on trees in the garden of Eden. So that sense of wealth, and of spiritual preciousness, were key factors in maintaining European interest in Asia.

How important were faith and spirituality in drawing people to Asia as Europe grew more powerful in the late medieval period?

During the period in which Christian Europe was at its peak of self-confidence, I don’t think Europeans expected that they would find much by way of wisdom in Asia. They were more interested in spectacle. There was a fascinating English traveller called Tom Coryate, for instance, who gained the nickname ‘the Legge-stretcher’ because in the early 1600s he walked most of the way to India. He wrote to his mother saying that he was looking forward to going to the Ganges, where he’d heard that there was a festival in which people threw “massey great lumps and wedges of gold into the river”. So what attracted him was a kind of heathen spectacle.

Europeans were also fascinated by Hindu temples with depictions of gods like Ganesha, because to their eyes they looked deliciously devilish and disgusting. So this was a kind of tourism.

But it’s also true that Jesuit missionaries out in India, China and Japan from the late 1500s onwards used Portuguese ships as a kind of global taxi service. They weren’t really trying to pick up any particular religious wisdom themselves, but realised that they needed to understand what people believed and speak their languages if they were going to have any hope of converting them. And what’s fascinating is that, in the course of doing that, they realised that those places were a lot deeper, spiritually speaking, than they’d anticipated. They had assumed that places in the world that hadn’t had a Christian revelation would, at best, have reached an ancient Roman-level, pagan sophistication. But they were really quite impressed, and some of the information that they sent back to Europe about these places – particularly China – started to garner the interest of Europeans.

Then, in later centuries, when Europeans began to have doubts about Christianity, they also found that there was much more wisdom available to them in Asia than they might have expected. By the 1700s, Europeans weren’t just interested in whether Asia might become Christian, but also whether Asia had something to teach Europe.

Which individuals were most important in bringing alternative ideas about how to make sense of the world from Asia to the west?

One of the key themes of my book is that western interest in Asia is almost always quite self-referential: how does it help us understand ourselves or critique our own societies? An example of this from the ancient era would be Cicero, who had heard of the custom of sati in India, in which a widow would throw herself on to her husband’s burning funeral pyre. He wasn’t so much interested in that as an aspect of Indian culture, as in making the point that Roman women didn’t show that kind of fidelity and commitment to their men.

Another, much later, example is that of Voltaire in the second half of the 1700s. He was particularly interested in China, having read reports sent back by the Jesuits. They were generally quite laudatory, because they wanted to promote China back in Europe as a place that was sophisticated and therefore ready for Christianity. So Voltaire’s impression of China, which he very influentially put about in Europe in his writings, was of a place that didn’t need priests or the church – which was good news for Voltaire, who considered the Catholic church to be pretty oppressive in all sorts of ways. Instead, he believed that people in China had a more direct understanding of God, that there were natural scientists interested in things like the stars, and that they lived in a society run not on family or clerical privilege but by a class of intellectuals – a bit like Voltaire himself. So in all kinds of ways, he imagined China to represent a perfect future for Europe.

The fact that China had survived as a successful society across so many centuries was really important for Voltaire, too, because a lot of people in Europe would say, well, you might want this kind of utopia, but it just can’t be done. And he could point to China as a concrete example of where they’d managed it, and which could be used as a template for reform in Europe.

Did the self-referential nature of this interest shape how western people were viewed in Asia?

Yes, I think so – and, by the 19th century, intellectuals in Asia were quite keen to play with Europeans’ self-referential interest in them.

In the second half of the 19th century, Japan was rapidly trying to modernise, and its intellectuals were really conscious of Europe’s technological and military advantage. But they were also pointing out that western technology, science, political forms and weapons were arriving in Japan from the west, representing a kind of cultural tidal wave. Their question became: what could be done to balance that out, to push back against this heavy cultural influence, and even to give something back to the west? And the idea they alighted upon was that western success had been bought at the cost of the western soul. Its people might understand nature, and be able to manipulate it through the natural sciences, for instance – but they didn’t have the deep access to nature that some of Japan’s Buddhist sects might offer. If that was the case, they thought, perhaps they could promote practices to westerners, such as those offered by Zen Buddhism, as a way of gaining direct access via nature to the deeper reality beyond.

As a result, people from Japan and India toured the United States and Britain, teaching meditation and yoga. It was as a way of saying, actually, Asia does have something to offer you – and that if your primary interest in Asia is what it can do for you, we’re going to take advantage of this and sell Asia back to you as a place of deep spiritual wisdom. And that’s something I think is still with us today, to some extent.

Are there darker aspects of the west’s fascination with Asia?

I think there are. In the late 18th and early 19th centuries, for instance, when Europeans became eager to find a kind of contemplative wisdom in India, there was a real danger of portraying its people in quite a racialised way as contemplative, passive, and lacking the kind of manly vigour celebrated elsewhere in European culture.

There was a political element, too, because this was the era in which the East India Company was gaining ever more territory in India. One of its key ideas was that India had a wonderful civilisation, which had been under the thumb of the Islamic Mughal empire for a couple of centuries, and now the English (and later, the British) had come to liberate people from its clutches and, in time, give them something better. So it fitted the political narrative to reinforce the idea of a contemplative, passive Indian society.

You see something similar in Japan: a lot of Europeans who went to Japan early on, in the late 19th century, saw it almost as a kind of Garden of Eden without industry or horrible smoky cities. These fantasies of the natural landscape, and those of Japanese people as kindly and easygoing, were again very self-referential and self-serving. Indeed, some Japanese critics in the early 20th century started to push back against it, stressing that this wasn’t how they imagined themselves in the modern world and that, if they started to, they might find themselves under the colonial thumb in a situation similar to that experienced by India.

Are there particular cultural works from the late 19th and 20th century that have proven surprisingly influential or that don’t get the attention they should?

An interesting cultural current is the rise of writers in Europe in the years after the First World War who suggested that the continent might be doomed if it didn’t come together with Asia. The shock of that conflict, its madness and carnage, had made people realise that the process of civilisation couldn’t be seen as a steady upward journey. Indeed, some people felt that it pointed to something deeply sick in 
the European soul – because, after all, it had seen European Christian powers fighting each other. As far as these writers were concerned, that sickness couldn’t be healed without an influx of Asian wisdom.

• Read more | First World War: beyond the western front

In the final section of the book, I explore the lives of a small group of people and the ways in which these wider themes played out in their lives. The 20th century was a period of spiritual odysseys: of people trying out all kinds of ideas and practices to see how they might benefit them. One of the people I focus on is Alan Watts, who had become very interested in Zen ideas during the 1930s and 40s. His argument was that religion ought to be considered in terms of mythology: as stories that somehow get at a deeper reality.

Christianity, he suggested, no longer worked as a system of mythology, because people had problems with some of its beliefs or had lost faith in its priests. He felt, however, that people in Asia understood how to treat a myth as a myth, and how to use those stories and their artwork to access a deeper reality. Watts argued that, by adopting such an approach, people in the west could either reinvigorate Christianity or start adopting practices such as Zen for themselves.

Watts wrote a series of books on Asian wisdom that were very influential. He managed to pitch it as being countercultural, and as providing a rich source for radically rethinking western society. His ideas really captured the imagination of the younger generations – who, by the 1950s and early 60s, were rebelling against their parents and wider social institutions. I don’t think he is terribly well remembered today, but his influence was huge.

How should we think about this story from our vantage point of the early 21st century?

If we bring the story up to the early 21st century, there’s probably a bit of pressure on me as a historian, writing across this huge span of time, to say where we might be heading next. And, although it’s not my job to look into some kind of crystal ball, I am really interested in where phenomena such as the wellness movement that’s taken off over the past few years fit into this story. A parallel I draw is with the story of Swami Vivekananda, an Indian teacher who visited the west a few times to teach yoga and share a broader, optimistic vision of Hinduism. He spoke at the 1893 World’s Parliament of Religions, a fascinating event held in Chicago in which many of the religions of the world came to speak about their traditions. It’s said anecdotally that the rooms would be packed for speakers from India, China and Japan, but when a Christian representative got up to speak you’d hear the sound of shuffling feet and slamming doors. People really were most interested in hearing something new and exotic.