Go west with Genghis and the plague, east with Buddha and Islam

The raw materials for this book - with all its faults and shortcomings - come from the Silk Road itself," explains Jonathan Tucker. So, arguably, do the hardships of reading it. It weighs about 3kg, which must be the same as a modest bundle of silks; the paper has such a heavy-gloss finish that the reader must constantly reposition himself to avoid its glare; and the prose mimics the terrain, with too much repetition, a monotony of emphasis and an unsparing aridity of expression.

Yet it is a most handsome volume, admirable in scope and reliable in detail. To those with the stamina for 2,000 years of history, 50 or 60 dynasties and half-a-dozen religions, all of them strung out along some 11,250km of now not-much-travelled trail, it will serve as a treasured compendium. Tucker is an art dealer who handles the Silk Road's kaleidoscope of Asian artefacts with insight and reverence. His research is impressive and his enthusiasm undisguised. "It would be no exaggeration," he confides in the preface, "if I were to tell you that my interest in the Silk Road borders on the obsessive, and has done so these past 20 years." One does not doubt it.

Most of those associated with the exploration of the Silk Road's sites, such as Sven Hedin, Aurel Stein and Albert von Le Coq, concentrated on the deserts of western China and parts of Afghanistan. Tucker takes on central Asia, from Mongolia to Mesopotamia, and adds for good measure Anatolia and the Levant. Given that, with a few exceptions, merchants of old seem rarely to have travelled more than month-long stages before exchanging their goods, he may have seen more of the trail than Alexander of Macedon and Marco Polo combined.

That he has visited most of the sites is evident from the superb collection of more than 400 photographs interspersed throughout the text. Nearly all are in colour and were taken by Tucker's wife, Antonia Tozer. The subjects are well chosen, the quality exceptional and the distribution exemplary. In fact, each page of text may more conveniently be read as an extended caption to accompany the photos that share its space. Just as the Tuckers presumably flew and drove to the sites, the reader, rather than slog through the dunes of typography, may find it more rewarding to home in on the history by way of the pictures.

Tucker's "obsession" is with the physical evidence - murals, statuettes, sun-bathed ruins, wind-scarred motifs, shreds of textile, shards of pottery and snatches of inscription. The geographical and historical distribution of these items is taken to establish the facts of East-West exchange and to illustrate its nature. He is not much concerned with the terms of commerce or the production of the commodities (including the silk), which are better dealt with in Frances Wood's book of the same name (2002). Nor, except to quote them, does he trouble with archaeological explorers and despoilers of the sites who in the late 19th and early 20th centuries gave currency to the term the "Silk Road". That epic of scholarly rapacity has been related by others, most notably by Peter Hopkirk in Foreign Devils on the Silk Road (1980).

More convincingly, Tucker's The Silk Road is not a highway but a broad corridor of territory, several hundred miles wide, stretching from China to the Mediterranean. His many maps show it as being crossed by a capillary of routes, seldom a single road; and his four tabulated pages of commodities, technologies and religions that travelled the road testify to a mutually advantageous exchange. If Europe's most prized import was silk, a luxury, for China the principal yield was horses, the motive equivalent of oil in pre-industrial times and a military necessity.

Tucker's listing of mechanical inventions that passed from China to the West by way of the Silk Road (or perhaps "Horse Road") is particularly impressive and ranges from the canal lock-gate to the wheelbarrow. More on the "square-pallet chain pump" and the "edge-runner mill" would have been welcome, as would something on how and when these transfers took place.

The doctrinal flow was largely in the opposite direction. Seemingly, Zoroastrianism, Buddhism, Nestorian Christianity, Manichaeism and the various forms of Islam all headed east. The West evidently had a surplus of belief systems and the Far East a deficit. Whether a few well-funded Chinese archaeological expeditions to the sites of, say, Iraq would have come up with evidence for the westward spread of Confucianism is an interesting question. As it is, the Far East seems to have reciprocated these devotional overtures only with unnecessarily harsh visitations, such as the Mongol invasions and the bubonic plague.

To the ebb and flow of ideas and merchandise, Tucker bravely adds the trickle of migration and the tramp of conquest. It is not always easy to distinguish the two, and his championship of the Sogdians of Samarkand, a ubiquitous and long-extant Caucasoid people, as peaceable craftsmen and consumate Silk Road traders may be misplaced. Alexander the Great found the Sogdians militarily formidable, and their reputation for responsible trade relies heavily on Stein's discovery of some much later "ancient letters" near the Great Wall. Fragmentary and difficult either to decipher or to date, it is on such chance and often-contentious finds that the history of the road has been reconstructed.

Ironically, the Silk Road was safest, and busiest, in the wake of conquest, whether Macedonian, Sassanian, Mongol or Timurid. The Mongols' greatest innovation may have been the passport, a badge of safe-conduct that was respected throughout their domains. Under the rule of Genghis Khan, according to one Muslim writer, central Asia in the 13th century "enjoyed such peace that a man might journey from the land of sunrise to the land of sunset with a golden platter upon his head and not suffer the least violence from anyone". This, in reverse and minus the golden platter, was what Marco Polo did at the end of the century. It was thanks to the Pax Mongolica that he survived to tell, and embellish, his tale.

Like Polo, Tucker structures his narrative of the greatest of the ancient world's overland routes round a progression, in this case from East to West. He begins at Xian in China and ends at Constantinople. Examination of each site and its artefacts creates a fascinating spectrum of cultures and styles, gradually blending into one another. But with so much history to incorporate, a chronological approach might have been better and would certainly have eliminated the need for so much factual repetition. The connoisseur of Asian art will not object and the historian should be able to handle it. But the general reader might do well to stick to the magnificent photos, savour their romance and be selective with the text.

John Keay is the author of many books on the areas covered by the Silk Road, most recently Sowing the Wind: The Seeds of Conflict in the Middle East .