High in the wilds of Kyrgyzstan, Colin Thubron - parfit gentil troubadour - takes shelter at the home of Nazira, a herdswoman. 'Of course it's hard here,' she says. 'It becomes very cold. But it's beautiful. The cat and me and the donkeys, in the silence. Just me - and now you too!'

This is the essence of travel, and the essence of Thubron's travel writing: to find somewhere untrammelled by the exigencies of modern life, and someone who revels in being surrounded by nothing but Nature.

Yet Shadow of the Silk Road is far more than a series of felicitous encounters, although Thubron's ability to discover and draw out people - monks, artists, warlords, verbose government statisticians - who can give voice to their experiences and speak for their kind and their generation is a recurrent joy.

Starting in China, he wends his way west to Antioch on the shores of the Mediterranean, encountering a variety of forms of Islam, crossing numerous borders, yet paying far more attention to the barriers of ethnicity, language and religion, and tracing the ebb and flow of ideas and inventions along the greatest land route on Earth.

Thubron, an inveterate traveller for the past four decades, has admitted in the past that he spends up to a year conducting research before setting out on a journey, and his bank of knowledge is phenomenal, allowing him to weave an adept course between past and present. 'To follow the Silk Road is to follow a ghost,' he writes. 'It is not a single way but many: a web of choices.'

The term Silk Road was coined by the 19th-century geographer, Friedrich von Richtofen, but it was never a single artery, rather a loose-knit series of corridors connecting the Orient and the Levant. Thubron strikes west out of Xian, skirting Tibet and the Taklamakan desert, forging through Central Asia past the Hindu Kush and on into Iran and Turkey.

His passage is by no means an easy one. China was plagued by Sars at the time of his travels, and at one point he's detained as a suspected casualty. He escapes death by inches at the hands of a drunken driver. And all the while, he shrugs off the danger and discomfort, and there's more than a little charm in this courtly old Etonian, shabbily dressed yet displaying a shining intellect, discoursing in Russian and Putonghua, so much concerned with the present yet firmly anchored in the past.

Thubron has a sharp eye for humorous incident, as well, recounting the furious argument in the wake of a semi legal rock concert in Tehran, between an official convinced that one of the images projected behind the stage was of a stream of sperm, while the band leader insisted it was tadpoles.

The lands Thubron passes through are in a state of upheaval, disrupted by rogue economics and political change. The consternation caused by a bellicose America is, he suggests, yet another example of the misunderstandings that have plagued the world since history began. At one stage the Romans believed silk came from a country called Seres, where it grew like a pale floss on multi-coloured flowers. In turn, the Chinese had heard rumours of a great city in the west, an amalgam of Rome, Alexandria and Constantinople, ruled by philosophers.

Jan Morris - no slouch in the field of memoirs from abroad - says of Thubron: 'This transcendentally gifted writer is, of course, one of the two or three best living travel writers, perhaps the best.' The only trouble with sacred cows is that they're sometimes tempted to moo. Silk Road is occasionally, but minutely, marred by imagined conversations with a Sogdian trader of yore, meanderings intended to shed light on the motives for his travel but which are a rare misjudgment.

That said, the rest of the book, alive from beginning to end with elegant, flawless prose, flows with an ease and vitality that belie the hardships the author must have suffered in the course of his odyssey.