It speaks volumes about the American spirit that the Rocky Mountains, or other purple mountain majesties or fruited plain, have never inspired an American poem as fine as Hart Crane's "The Bridge," a hymn to the Brooklyn Bridge. Only God can make a mountain, but he has made so many. The West could call for men to match its mountains, but New York City would build urban mountains, beginning with the bridge that is now a century old.

It linked America's first and third largest cities (Brooklyn was independent until 1898) by vaulting a river--the East River--that is not a river but a tidal strait of salt water. Persons uneasy with any but banal explanations can say that the motivation for building the bridge was economic: the raising of property values in Brooklyn. But from the first conception, the bridge was an expression of the intangible beneath the tangible in America, the heroism of what has been called America's heroic materialism.

Writing in the 1860s about America's industrial energies, Walt Whitman exclaimed: The shapes arise! Shapes of factories, arsenals, foundries, markets, Shapes of the two-threaded tracks of railroads, Shapes of the sleepers of bridges, vast frame

works, girders, arches.

Today, environmentalists would want Whitman to file an environmental impact statement with his poetry. Whitman, a Brooklyn boy, was fond of "singing the strong, light works of engineers." Today, intellectuals are inclined to resent the presence of machines in the American garden. A century ago the works of engineers seemed not a desecration of "nature" but an affirmation of the human drive to conceive and achieve. "Not one shall see it and not feel prouder to be a man," said a speaker at the opening of the bridge, May 24, 1883.

The bridge has had not only a magnificent poet in Hart Crane, who died at the age of 32 in 1932, but also a marvelous biographer in David McCullough. Of no other American artifact, save possibly the Tennessee Valley Authority, can this be said: its biography is the biography of an era. McCullough's theme is that any great achievement is a product of a great passion, in this case a passion for projects of great scale with utility proportionate to scale.

Today the biggest things mankind manufactures are either repetitious (Chicago's Sears Tower is bigger but no grander than the Empire State Building), diminishing (Manhattan's dispiriting canyons) or appalling (nuclear explosions). Today's excitement is on small frontiers--atoms, chromosomes. The 19th century thought big was beautiful: a big nation ("manifest destiny") with big ligaments (bridges, transcontinental railroads).

Crane compared the bridge to a harp. That is the sort of vision that, when a poet has it, becomes accessible to those of us who have more prosaic sensibilities. The cables are the harp's strings; the tensions in equipoise give the instrument harmony. A harp or violin is beautiful because it is the purest submission of form to function. Only America's clipper ships compare with America's bridges, and perhaps a few Western dams, as works of physical beauty.

Built of the ancient and modern materials-- stone and steel--the bridge has been called an architecture of voids rather than solids. It was the first vision of the New World for millions of immigrants. Its twin towers were New York's first skyscrapers. In 1883 only the spire of Trinity church in Wall Street was taller. The towers' gothic arches were suited to this, our Notre Dame, our cathedral for the secular city. This vaulting creation expressed America's defining urge, the itch to get up, get moving, get across, get on the road.

It is a measure of how far we have come that today we have no sense of how far it was across the East River 100 years ago. Our proficiencies have cost us our capacity for wonder: no physical attainment, not even space exploration, excites Americans today the way dozens of things--bridges, tunnels, ships--excited Americans then.

In 1876, the Centennial was resolutely forward- looking. Its centerpiece was the Philadelphia exposition of the latest machinery. In 1976, the Bicentennial had a retrospective cast. The highlight was a parade of Tall Ships, elegant echoes of a vanished age of dash and daring. Perhaps this was a symptom of flinching from a daunting future; if so, it was sterile nostalgia. However, today's keen interest in the great bridge's birthday may be exactly what this nation, and not least New York City, needs: an unthought but deeply felt impulse to rekindle confidence in our capacity for great works.