In recent times, architectural "style" seems to resemble the weather. Wait a bit, and it changes, whether you like it or not.

What's new and interesting today may seem stale and boring tomorrow. Aesthetic values change periodically as stylistic gestures emerge, find advocates, gain public acceptance, become cliches and are finally condemned and rejected by proponents of the next stylistic revolution.

Until the end of the 18th century, American architectural styles were fairly unpretentious. Only occasionally did buildings display touches of applied decoration that might lift them out of the realm of vernacular, regional architecture. And when that occurred, Americans went, figuratively, to Europe.

Eighteenth century Europe was unquestionably the cultural mecca of western civilization. Although many colonists believed America would be the land of unprecedented political and economic opportunity, Europe remained the undisputed source of precedent and inspiration for art, music, literature and architecture.

So, while Americans were busy exploring and exploiting the New World, Europeans of the 1700's were rediscovering the ancient worlds of Greece and Rome, just as they had during the Renaissance of the 15th and 16th centuries. Given the exuberance and occasional excesses of late-17th century Baroque and 18th century Rococo architecture, classically inspired purging and purification seemed inevitable.

To rational minds in the new scientific age, Greek and Roman classicism was more orderly, logical, systematic, and therefore symbolically appropriate. Resurrected again were academic styles that contrasted sharply with those of the romantic, ethereal, post-Renaissance era.

What are the familiar hallmarks of this historical classicism, first developed over two millenia ago and continually rediscovered? The austere Doric order of Greek and Roman temple facades contains the basic elements. A triangular pediment, ending the roof, sits atop a large, horizontal lintel, the entabulature. In turn, the entabulature is supported by several columns sitting on a base and forming a portico, or porch.

Looking more closely, one discovers other layers of composition where surfaces and joints gain definition. The columns are fluted, tapering gradually toward a capital -- a simple, round molding and a flat, square slab. The entablature is divided horizontally by moldings to create a cornice with a frieze (alternating "triglyphs" and "metopes") and architrave below. Precise, modular dimensional relationships govern sizes of columns, spaces between columns, and entablature components.

Other classical orders were more elaborate as Roman designers gave columns individual bases and fancier capitals (the scroll-like Ionic and leafy Corinthian being the most familiar). Entablatures and pediments became more ornate and occasionally fragmented. These elements could be imprinted onto virtually any surface, or around any kind of opening. Equally important, Romans used circular arches and domes. The Greeks had employed only wood beams, trusses and stone lintels to span space.

The naive, picturesque beauty of English or American vernacular could never compete with architectural symbols and formulas derived from civilizations that historians and philosophers persisted in idealizing and idolizing.

The writings of the Roman architect Vitruvius, who set forth clearly and uniquely the virtues and principles of Roman architectural composition, in turn inspired the great 16th century Italian architect Andrea Palladio to update and reinterpret those principles. In so doing, Palladio invented his own, widely influencing European building styles, particularly in England.

To Americans like Thomas Jefferson, who was familiar with such theories and had visited Europe, the adapted classicism of Vitruvius and Palladio was just what the new republic needed. England's yoke was gladly thrown off, but not its classical architectural heritage. This heritage both predated and survived the American Revolution. Visiting Georgetown, Capitol Hill, or Alexandria today, you still see "Georgian" and "Federal" styles of the late 1700's and early 1800's. They are represented by buildings of simple overall mass with understated but classical details, as if still clinging to the unpretentiousness of early American building while striving for European refinement.

But as the 19th century began, when the classic revival was well under way in Europe, American architects -- William Thornton, Charles Bulfinch, Benjamin Latrobe, James Hoban, Robert Mills -- decided that the relative calm of Georgian architecture wouldn't be adequate to express American, democratic aspirations; these could be embodied only in the explicit, revivable architecture of Greece and Rome.

The U.S. Capitol building, despite its many transfigurations by feuding designers, reflects clearly the continuing thread of classicism woven into Washington's monumental public buildings.

Indeed, for the first half of the 18th century in Washington, the sanctioned style was classic revival in one guise or another. You see it in the Doric-style St. John's Church on 16th Street and the Custis-Lee Mansion at Arlington Cemetery, in the Ionic-style Treasury Building next to the White House, and in the Old Patent Office.

Of course, it didn't last. At mid-century, it was time for a romantic revival. One only had to wait for the cycle of novelty and boredom to repeat itself.