t's been a roller-coaster century in architecture. We've seen some of the greatest stuff ever, and a lot of the worst. Here in the United States, we've enjoyed the work of an all-time genius, Frank Lloyd Wright. But especially in the second half of the century, we've lived in an era when building is often seen as mere packaging. If architecture is an art - the greatest art, some have claimed - then too many buildings today look like the packing crate the art must have come in. Or else, especially if they are private houses, they too often look like inept reproductions of styles that once, long ago, were alive.
Any way you sum up a century is going to be simplistic. But if you had to characterize the 20th century in a single title, you'd have to call it ''The Modern Movement and Its Enemies.''
Modernism arose in architecture around the time of the First World War, roughly the same time it was breaking through in music, dance, painting, and literature. For a long time it was the province of a tiny avant-garde. Eventually it dominated. But a lot of people, including architects, didn't like Modernism and still don't. They revived historic styles, supported the preservation movement, or embraced semi-modern architecture such as Art Deco.
What, exactly, is Modernism? The short answer used to be: It's architecture in which Form Follows Function, so-called functionalism. But that identification is now regarded as pretty much a myth. Once we built enough of them, it became clear that modern buildings, though they could sometimes be very beautiful, typically didn't function any better than older ones.
I'd say there are three basic clues to Modernism in architecture:
Modernism accepted the principle of the avant-garde that newer is better and revolution is healthy. Deep down, it's a Marxist view. ''Old-fashioned'' became synonymous with ''bad,'' a concept no one would have understood in previous centuries. Architecture was supposed to be ''advanced.'' New techniques and materials - think of steel, glass, and concrete - were adopted not only because they were sometimes practical, but also because they were seen as emblems of progress.
Modernism, in its pure form, more or less ignored the conventional language of architecture. As the architect Charles Moore brilliantly put it, Modernist architects chose to speak in Esperanto: an invented language, one that lacks the cultural resonance of a real language that has accumulated rich layers of meaning over time. Before Modernism, a bank probably had a row of Roman columns in front and maybe a dome. That was a visual language, a sort of iconography, that bespoke ''Bank'' almost as clearly as a billboard. After Modernism, a bank might be a glass box, indistinguishable from a shoe store or a health clinic. Ornament, too, seen as meaningless decor, was eliminated from new buildings. Architecture became more abstract - which brings us to Clue No. 3.
Modernism took its visual cues from the other arts, especially painting. In the 20th century, painting faced a crisis. It needed to reinvent itself. A new technology called photography was doing one job that painting had done, of representing the real world. So paintings became abstract. They began to represent nothing beyond themselves. There's nothing really new about that - a Persian carpet is abstract art, too - but it was a new idea for Western painting, and it felt dynamic. The first and most important abstract movement was Cubism, invented by Picasso and Braque before 1910. Cubism became the dominant motif of Modernist architecture. Right angles, thin planes, transparent surfaces, flat roofs, and anonymous materials (often white) replaced the heavily constructed walls, sloped or vaulted roofs, tangible materials, and handicraft of the past.
Of course I'm oversimplifying like mad. And I've left out the political side of Modernism. That was its social agenda. Most of the early moderns were idealists who truly believed the new architecture would house the poor and make the world a happier, more rational place. But over time, the social idealism dropped away. As early as the exhibition called ''The International Style'' - the 1932 event at the Museum of Modern Art in New York that brought modern architecture to America - Modernism was being touted largely as an esthetic style, like abstract painting.
By the 1950s, Modernism had triumphed, but often in a sadly debilitated form. Developers realized that those simple boxlike forms, without craftsmanship or ornament, could be built cheaply. As Modernism cheapened and spread, a rebellion sprang up in the 1970s and '80s. Called Post-Modernism, it revived various styles of the past, usually in a tongue-in-cheek, deliberately ironic, obviously stagy manner that was intended to make architecture fun. The 1990s, by contrast, have seen a counterrevolution, a return to Modernism with a new recognition of the enduring power of this austere architecture when it's well done.
I've been asked to list 10 watershed events or works of the 20th century in architecture. Listing 100 would be easier, but here's a stab, in rough chronological order.
1) The Bauhaus, founded in Weimar, Germany, in 1919. Walter Gropius and Mies van der Rohe, two of the most influential architects of the century, each headed this school for artists and architects at different times. After the rise of Hitler, both emigrated to the United States, where they spread the gospel of Modernism - Gropius as a teacher at Harvard, Mies as the architect of such icons as the Seagram Building in New York. The Bauhaus lasted for only a dozen years, but its ideas changed the world.
2) ''Towards a New Architecture''(1923), by Le Corbusier (whose real name was Charles-Edouard Jeanneret, and who was himself a gifted abstract painter). Corbusier's breathlessly messianic prose style and vivid drawings and photos made his book the best propaganda ever for Modernist ideas. Corbusier went on to become one of the two or three great architects of the century, creating classics like the chapel at Ronchamp and the monastery of La Tourette, both in France. The book also foreshadows Corbusier's disastrously influential ideas about city planning. Instead of traditional cities with their intimate, humanly scaled streets, Corbusier believed in a world of superhighways slicing through endless parklands, where large buildings stood in lonely isolation from one another. It's pretty much the world of freeways, highrise housing, office parks, and shopping malls we later built.
3) ''Garden Cities of Tomorrow''(1902), by Ebenezer Howard. Maybe it seems strange to give so many places on the list to books, but this has been a century in which architecture, like so much else, has grown from ideologies and clashing manifestos. Howard's vision of a compact, self-contained, sprawl-free suburban paradise led directly to today's ''New Urbanism'' - an anti-Corbusian movement - as demonstrated in such recent model communities as Seaside and Celebration in Florida.
4) The automobile. Especially after we built the interstate highway system to accommodate it, the automobile generated endlessly sprawling settlement patterns. It drained center cities of much of their life and isolated Americans from one another (whether in the steel capsule of the car itself, or in the thinly spread-out communities it made possible). Cities and towns are collections of buildings with some relationship to one another. By scattering us across the countryside, the automobile made architecture less important in most people's lives.
5) Frank Lloyd Wright. Wright was a Modernist who never lost faith in the importance of natural materials and human scale. His many triumphs include Fallingwater in Pennsylvania (the most famous house of the century); his own two houses, Taliesin West in Arizona and Taliesin East (perhaps his masterpiece) in Wisconsin; and such public buildings as Unity Temple in Chicago and the Guggenheim Museum in New York. Like other Modernists, Wright fell too much in love with the automobile. But Wright - together with his Finnish counterpart Alvar Aalto - cared deeply about the full range of human experience and about the relation of architecture to the forces of nature. They're probably the 20th-century architects you'd most like to see remain influential in the 21st.
6) ''The Death and Life of Great American Cities''(1961), by Jane Jacobs. The third great and influential book on the subject of how we build and live. It's by far the most powerful attack on Corbusian planning principles. Today's revival of interest in city life, with all its variety and density and unpredictability, is partly attributable to Jacobs.
7) Demolition of Pennsylvania Station, New York (1963). The loss of McKim, Mead & White's masterpiece was significant in itself, but even more important was the way it spurred the emergence of the historic-preservation movement. New York City created its Landmark Preservation Commission in 1965, and the watershed National Historic Preservation Act followed in 1966. Never again would Americans allow their architectural heritage to be so blithely ignored.
8) The Kimbell Museum(1972) in Fort Worth, the masterpiece of Louis Kahn. The Estonia-born Philadelphian became America's - perhaps the world's - greatest architect of the 1960s and '70s. His Kimbell is probably the best US building of the post-Wright half of the century.
9) The sustainability movement. Maybe that's not the best name for it. ''Green architecture'' is another, much used in Europe. Sustainable architecture is shorthand for building in a way that won't drain the planet of its resources, nor destroy its climate. It worries about appropriate patterns of settlement and about architectural materials and methods. As we look to the next millennium, it seems obvious that survival of life on Earth will be a dominant political issue. The sustainabilty movement, now rapidly growing, is cause for hope.
10) The Guggenheim Museum in Bilbao, Spain(1997). New movements in architecture are often inspired by new technology. Frank Gehry's Guggenheim, with its roof of titanium that billows like a fleet of spinnakers, could not have been designed - nor could it have been constructed - without the aid of the computer. Computers, however, are just as good at generating pallid imitations of Spanish Colonial, or any other style. Their final influence remains to be seen. But as of now, it seems likely that the Guggenheim will be remembered as the moment, at the end of a millennium, when we crossed the threshold to a new kind of architecture.
