THE LAST BARBARIANS: The Discovery of the Source of the Mekong in Tibet.

By Michel Peissel. Henry Holt. 320 pages. $27.50

Michel Peissel would have been world famous in an earlier century, but he is an explorer at a time when, as he writes, "most people think explorers are old-fashioned or completely obsolete." In The Last Barbarians, his 15th book, he makes a triumphant case for the explorer, weaving history, geology, and politics with candid revelations of the yearnings and ambitions that have carried him to some of the remotest places on the planet.

A fluent Tibetan-speaker with more than 37 trips to the Himalayas behind him, Peissel discovered in his reading that the source of the Mekong River had never been established. (The French explorer Dutreuil de Rhins, leader of an 1894 expedition up the Mekong, was shot to death by Tibetan tribesmen in a dispute over stolen horses before reaching the source.) Mindful that success would bring little glory or money, and that an intransigent Chinese bureaucracy would make securing travel permits anything but easy, he was spurred on by his respect both for the Mekong (Asia’s thirdlongest river, originating in Tibet, crossing China, India, Laos, Myanmar, and Thailand, and ending at a delta in Vietnam) and for Tibet’s ecological primacy as the riverhead of Asia, the source of the Yellow, Yangtze, Salween, Mekong, Bramaputra, Irawaddy, and Ganges rivers.

The author is painfully witty in describing the hell of innumerable days in a Land Rover, referring to himself as "strictly what you might call a foot and horse man" who is trapped with a driver, two companions, and a humorless and unenthusiastic Chinese guide. At an outpost, they barter for porters and horses. Then, after a 15-day journey, they reach the object of their quest, the headwaters of the great Mekong—which prove to be not a stupendous glacier, like the source of the Ganges, but a mere trickle from a patch of red soil. "We had discovered the source of the Mekong, an act as banal as it proved to be magical. There was little or nothing to see. The true importance of our discovery was all in the mind, for we had reached one of those rare sacred places where myth and reality meet."

Crossing the vast Tibetan highlands back toward civilization, where he confronts the ugly reality of the Chinese military occupation (in place since 1950), Peissel ruminates on whether technology has divided man from nature and robbed us of willpower, curiosity, and wonder. His mission has become an exploration of the conflict between the civilized and the nomadic: "There is nothing organized society fears more than the intrusion of smart, carefree, gutsy, horseback-riding ‘barbarians’." Once more Peissel has proved that even in the age of the satellite and the Internet, there are yet many things about our planet that remain unknown.

—Maura Moynihan