The Spice Route covers a lot of charted territory, but it's one of the clearest explanations to date of the oldest example of global trade and its cultural and political ramifications.

'In ages past, when utility was paramount, the allure of spices lay precisely in their glorious irrelevance,' Keay writes. 'Rare enough to imply distinction and distinctive enough to be unmistakable, spices unashamedly announced themselves as luxuries.'

The Greeks and Romans, the Egyptians and Ethiopians, Phoenicians and Arabs, all engaged in the spice trade. The early Roman empire was sending 200 ships a year, each capable of carrying 500 tonnes of cargo, a trade unmatched until the 15th century. There were all the fluctuations in commodity prices expected of a sophisticated exchange, with the price of high-grade cinnamon bark highly sensitive to supply.

It was business, and Pliny reckons Rome was running an annual trade deficit of 100 million sesterces, or about 10,000kg of gold, more than the output of its new mines in Spain.

This was 'a significant drain on the imperial exchequer and was sustainable only as long as the empire's legions continued to bring in the treasure and tribute of neighbouring territories,' Keay writes. 'Once these declined, and new mineral discoveries ceased, Rome would be

in trouble.'

It had developed a taste for spiced ostrich, curried crane and peppered parrot.

Meanwhile, for every vessel with peppercorns headed west, 10 went to China. The Han were doing business early in the first millennium with merchants from as far off as Syria.

Chinese and Arab ships freely plied the spice route well into the second millennium, until a rather nasty Portuguese named Vasco da Gamma swept into the Indian Ocean.

His attempts to curry favour with cheap trinkets from his dinky 100-tonne ships merely offended a people more used to a rich trade with China and its mighty 2,000-tonners. Many were Muslim, so da Gamma decided to liberate the spice route for Christendom, with cannon fire replacing the clink of coin.

Had China not decided, just as it had control of the spice route in its grasp, to withdraw and burn its mighty fleets, da Gamma might have been seen off.

The significance of the spice route peters out with the various takeover bids by the Dutch, British and French.

In the end, commercial realities debased the whole business and the luxury status of spice was spent, although the Dutch did manage to swap Manhattan in exchange for an unfettered hand in the East Indies and finally found the mysterious islands where the spice route began.

Keay sifts the historical facts, setting the record straight on a number of points, and even taking gentle issue with one fellow writer who has made sweeping claims about the reach of China's exploration.

'Only in calling such claims 'epoch-making' does the book advancing them understate its case,' he says, leaving the reader to flip to the endnotes to confirm the target of his comment.

Keay also posits a disturbing question: Which came first, the chicken or the masala?