Coming from a historian who wrote an Armada book for 1988, a life of Columbus ahead of the quincentennial of 1492, and a study of Amerigo Vespucci in time for the 500th anniversary of the naming of America, what I'm about to say may sound incredible.

I can see no reason - except superstition or pointless adherence to tradition - for commemorating events at intervals of decades and centuries.

In writing those books, I was responding to public interest, not endorsing its irrational quirks. I'd be as happy celebrating a memory every 42 or 395 years, say, as every 40 or 400. When we engage in these commemorations, moreover, we often seem to choose the wrong event.

This year, in most of the Western world, the 40th anniversary of a reputed annus mirabilis has captured most of the attention of the commemoration industry. But 1968 seems unworthy: a year of false hopes, failed dreams and dispiriting deaths.

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In Spain, people are marking, with varying degrees of enthusiasm, the 200th anniversary of the so-called War of Independence - the uprising against Napoleon that Goya painted so vividly. The war was a disaster, igniting Spanish nationalism, empowering the army, installing a reactionary regime and provoking Spanish America into rebellion.

But in all of this, the world has missed the chance to commemorate 2008's most noteworthy anniversary: 500 years since the birth of Andres de Urdaneta. The only celebrations I know of are taking place in Urdaneta's native Basque country, yet his achievement was of universal significance.

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He was the son of the mayor of Ordizia, a charming, stately, stone-built town overlooked by a spectacular, sharp-peaked mountain. News of explorers' exploits filled his boyhood with visions of glory.

When he was 17 years old, he sailed with one of the longest, deadliest, most gruelling expeditions in the history of seafaring - Spain's attempt to open commerce with Asia by way of the Pacific.

He recorded the deaths of three successive commanders and spent nine years in the Spice Islands, learning the natives' sea-lore. When he found his way home, he brought back key strategic intelligence, and the daughter a Malay girl had borne him.

At the age of 42, sated with adventure and having raised his daughter to marriage, he joined the Augustinian Order and became a priest. A decade later, though, the King called him from the cloister for a final adventure. Only Urdaneta knew enough about the eastern seas to lead the perilous new expedition.

Its objective was to cross the Pacific in both directions. No one had ever managed it before. The Polynesians, the greatest natural navigators in the world, had roamed the ocean for centuries without ever attaining its limits.

For two generations, Spaniards had launched a series of efforts in the path of the trade winds of the Pacific, but no navigator had been able to find the way back from Asia to America.

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Urdaneta, however, had already cracked the code of the winds and currents in his own mind. He knew that timing was critical: the expedition would leave the Philippines with the favourable monsoon, heading north with the current as far as the latitudes of Japan, where there were westerly winds, before steering for America and following a southbound current along the coast of what is now Oregon and California to Acapulco Bay.

Although Urdaneta wanted to live out his remaining years in his religious vocation, he could not refuse the King's command. He specified, however, that if Spain succeeded in opening up the Pacific it must be for the sake of evangelising the inhabitants, not fighting or exploiting them.

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His success, after three months on the open sea at the limits of his crew's endurance and the capability of ships of the time, really did inaugurate a new era. The route he established endured, with few improvements, as the only viable way across the ocean for the rest of the age of sail and remained dominant even when fuel-powered ships took over.

Without it, the world-girdling commerce of the Early Modern era would have been impossible. Cultural, commercial and ecological exchanges between Asia and the Americas would have been postponed. Urdaneta shrank an unnavigable planet to manageable dimensions of time and space and put long-sundered civilisations back in touch with each other.

Yet he remains in oblivion. Even in his quincentenary year, the world is unaware of how much it owes him.

If we are to have a commemorations industry, it should be better informed. The media know only about impending opportunities to commemorate what is already familiar - and which therefore hardly needs commemorating. Politicians notice only the opportunities that suit their agendas.

If the initiative remains exclusively theirs, the sum total of human knowledge will remain stagnant, and commemorations will continue to be warped by partisanship.

At the moment, academics' role is reactive rather than proactive, and limited to attempts to mop up mistakes by the media and to bust the politicians' myths.

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Academic institutions should get together to set up a worldwide watchdog, with responsibility for flagging up worthy anniversaries and exciting interest in good time. Commemorations might then cease to be tediously predictable and become truly instructive.