I slid down the dune and made my way through a defile and toward a hedge and an irrigation canal, beyond which were fields and orchards and grassy meadows, already being worked by men with the broad, flat faces of the Uighurs, whose country this was. Camels were grazing, hobbled and bad-tempered, and were being rounded up to take visitors on caravans into the sand and over to the caves. After all those miles of stillness and sand, Dunhuang was lively, bustling—and green.

It is also the Silk Road's most important junction, a place where the merchants and pilgrims of centuries ago had to decide whether to pass to the north or to the south of that most fearsome stretch of Chinese desert known as the Taklamakan. If they were heading toward India and Arabia, the southern route was better; if bound for Antioch and the Mediterranean, they would strike out to the north. It was at Dunhuang that, on the outbound journey, travelers would rest and decide; it was at Dunhuang that, on the way home, they would rest and give thanks for having survived.

Buddhists in particular offered thanks. They did so at three specific sites near Dunhuang, in gorges where the cliffs were tall enough and wide enough to allow the creation of what Indian Buddhists had long before shown a liking for: scores upon scores of intricately decorated caves, designed specifically for their mendicants and meditations. Of the three sites, by far the largest and most important was the mile-long cliff at a place called Mogao. Wandering monks began incising caves into the soft sandstone cliffs of Mogao in the fourth century, and by the time the last cave was dug in the fourteenth, more than a thousand of them had been created—some as tiny as coffins and made for sleep and shelter, some many stories high and used for worship and salutation. It is this that Aurel Stein reached in the spring of 1907.

He had left his base in Kashmir the previous year, and he had prepared well: books in tin-lined cases to protect them from ants, surveying instruments, ropes, leather-repair kits, bamboo poles for the tents, plenty of guns and ammunition, telescopes, elastic bands and paper clips, bandages, needles, safety pins, and a morning coat and pin-striped pants so that he might impress any mandarins he encountered. He left behind birthday presents for all the friends he would miss while away, and he packed plenty of food for Dash. He was a scrupulous man.

It took him half a year to reach the interior of China, and for most of the winter of 1907 he negotiated the harsh deserts of Turkistan. During February and March, Stein pushed eastward across the immensity of the Lop Desert (where in more recent times China tested its atom bombs), with his men on donkeys and camels and with ice blocks carried in straw baskets in lieu of water. One day in late March, an icy storm known in Turkistan as a buran was blowing a full gale, chilling everyone to the bone. The donkeys had died, the water was almost gone. And then suddenly he reached the oasis, and a few miles farther on—for he was headed for the cliffs before everything else, and wanted to waste no time for idle refreshment—he came to Mogao and the caves.