The man who ruled a fifth of the mediaeval world left his mark forever on a big part of it

The other error that Columbus carried off into the Atlantic with him, besides thinking he was going to reach China, was believing that Kublai Khan would be there to welcome him.

Of course the Mongol ruler of China, Korea, Pakistan, Iran, Georgia, Armenia, Azerbaijan, much of Russia, most of Turkey and half of Poland had been dead for two centuries by then, but the eclipse of his empire following his death had extinguished the light by which Europe saw the Far East.

Westerners were left to assume that the Great Khan depicted by Marco Polo was eternal and still on his bejewelled throne, hidden behind the wall that Islam had built.

Marco's travelogue, despite its many dubious claims, figures heavily in John Man's second visit with the Mongol emperors following 2005's "Genghis Khan - Life, Death and Restoration", but Man loves the science and the fact of the family history more.

With a style that's entrancing if not as poetic as his earlier book, he sifts through the ruins and the parchments and comes up with another trove of illuminating gems.

Among the most engaging are his long forays into the Mongol army's giant catapults, known as trebuchets, and its ill-fated invasion of Japan, wrecked not so much by divine kamikaze winds as by sloppy planning. It's astonishing to be among the Japanese researchers who are still squeezing bits of Kublai's battleships out of the murk at the bottom of Hakata Bay.

Also gripping is the tale of another doomed invasion, foiled by those darned Vietnamese guerrillas, and Man's assessment of Tibet's motley history, in which he clarifies much about modern China's claim to it. (Actually, by one interpretation, Tibet ought to be claiming China.)

Most edifying of all, and encompassing the Tibet question, are Man's conclusions about what exactly constituted China in Kublai's time and what it's become today. This is a history book that's just as important in the present.