It's worth pointing out that very few buildings (especially churches) were built in one particular architectural style. These massive, expensive structures often took centuries to complete, during which time tastes would change and plans would be altered.
Ancient Roman (125 B.C.-A.D. 450)
France was Rome's first transalpine conquest, and the legions of Julius Caesar quickly subdued the Celtic tribes across France, converting it into Roman Gaul and importing Roman building concepts. Except for the Parvis Archaeological Excavations of the Romanized village of Lutétia (later renamed after its native Parisii tribe of Celtic Gauls), very little remains in Paris. These excavations are under place du Parvis in front of Notre-Dame. Musée de Cluny, a medieval monastery, was built on top of a Roman baths complex, remnants of which are still visible on the grounds outside and in the huge preserved frigidarium (the cold-water bath), which is now a room of the museum.
The Romanesque style took its inspiration from ancient Rome (hence the name). Early Christians in Italy had adapted the basilica (ancient Roman law-court buildings) to become churches. Few examples of the Romanesque style remain in Paris, however, with most churches having been rebuilt in later eras.
The best remaining example of this style is on the Left Bank at the church of St-Germain-des-Prés. The overall building is Romanesque, including the fine sculpted column capitals near the entrance of the left aisle; only the far left corner is original, the others are copies.
By the 12th century, engineering developments freed church architecture from the heavy, thick walls of Romanesque structures and allowed ceilings to soar, walls to thin, and windows to proliferate. Gothic interiors enticed churchgoers' gazes upward to high ceilings filled with light. Graceful buttresses and spires soared above town centers.
The best examples in and around Paris of the Gothic are: Basilique St-Denis (1140-44), the world's first Gothic cathedral in a Paris suburb; Cathédrale de Chartres (1194-1220), a Gothic masterpiece with some 150 glorious stained-glass windows; and, of course, Cathédrale de Notre-Dame (1163-1250), which possesses pinnacled flying buttresses, a trio of France's best rose windows, good portal carvings, a choir screen of deeply carved reliefs, and spiffy gargoyles.
The Musée de Cluny combines magnificent gothic and renaissance elements in its facade.
In architecture, the Renaissance style stressed proportion, order, classical inspiration, and precision to create unified, balanced structures.
The best examples are: Hôtel Carnavalet (1544), a Renaissance mansion, the only 16th-century hotel left in Paris; and Place des Vosges (1605), a square is lined by Renaissance mansions rising above a lovely arcaded corridor that wraps all the way around.
Classicism & Rococo (1630-1800)
During the reign of Louis XIV, art and architecture were subservient to political ends. Buildings were grandiose and severely ordered on the Versailles model. Opulence was saved for interior decoration, which increasingly (especially 1715-50, after the death of Louis XIV) became an excessively detailed and self-indulgent rococo (rocaille in French).
Rococo tastes didn't last long, though, and soon a neoclassical movement was raising structures, such as Paris's Panthéon (1758), which were even more strictly based on ancient models.
The best examples include: Palais du Louvre (1650-70), a collaborative classical masterpiece, designed as a palace with Le Vau (1612-70) as its chief architect, along with collaborators such as François Mansart (1598-1666); Versailles (1669-85), Europe's grandest palace, the Divine Monarchy writ as a statement of fussily decorative, politically charged classical architecture, though the interior was redecorated in more flamboyant styles; and the Panthéon (1758), a Left Bank perfect example of the strict neoclassical style.
The 19th Century
Architectural styles in 19th-century Paris were eclectic, beginning in a severe classical mode and ending with an identity crisis torn between Industrial Age technology and Art Nouveau organic.
Identifiable styles include the neoclassical First Empire with its strong lines often accented with a simple curve -- the rage during Napoleon's reign; and Second Empire, which occurred during Napoleon III's reign, a reinterpretation of classicism in an ornate mood. During this period Paris became a city of wide boulevards, courtesy of Baron Georges-Eugène Haussmann (1809-91), commissioned by Napoleon III in 1852 to redesign the city. Haussmann lined the boulevards with simple, six-story apartment blocks, such as elongated 18th-century town houses with continuous balconies wrapping around the third and sixth floors and mansard roofs with dormer windows.
The Third Republic expositions in 1878, 1889, and 1900 used the engineering prowess of the Industrial Revolution to produce such Parisian monuments as the Tour Eiffel and Sacré-Coeur.
Art Nouveau architects and decorators rebelled against the Third Republic era of mass production by creating asymmetrical, curvaceous designs based on organic inspiration (plants and flowers) in such mediums as wrought iron, stained glass, and tile.
The best examples are the Arc de Triomphe (1836), Napoleon's oversize imitation of a Roman triumphal arch, the ultimate paean to the classic era; Tour Eiffel (1889), which Gustave Eiffel (1832-1923) slapped together to form the world's tallest structure at 320m (1,050 ft.); and Métro station entrances.
The 20th Century
France commissioned some ambitious architectural projects in the last century, most of them the grand projets of the late François Mitterrand. The majority were considered controversial or even offensive when completed.
At Centre Pompidou (1977), Britisher Richard Rogers (b. 1933) and Italian Renzo Piano (b. 1937) turned architecture inside out -- literally -- to craft Paris's eye-popping modern-art museum, with exposed pipes, steel supports, and plastic-tube escalators wrapping around the exterior; Louvre's glass pyramids (1989), were created by Chinese-American architect I. M. Pei (b. 1917); Opéra Bastille (1989), is a curvaceous, dark glass mound of space designed by Canadian Carlos Ott.
Paris’s Best Architectural Landmarks
* Best monuments to La Gloire (the glory of France): The Arc de Triomphe—the world’s largest triumphal arch —is about as grandiose as it gets, at least until you arrive at the magnificent Place de la Concorde, another grandiose national gesture. If that’s not enough, the church of La Madeleine was originally meant to be a temple to military glory, and the Panthéon is a church made into a crypt for the nation’s heroes.
* Best monuments to spiritual glory: Despite the French obsession with keeping the Republic secular, the capital harbors some of the world’s most exquisite churches. No matter what your views are on religion, you’ll be bowled over by the soaring arches of the Cathedral of Notre-Dame the stained glass of Sainte-Chapelle, or the superb rood screen at St-Etienne du Mont.
* Best monuments to human ingenuity: Extraordinary engineers and architects have spent time in this city, leaving behind some amazing buildings in their wake. Most famously, the Eiffel Tower, gracefully reaches for the sky, while exerting minimal pressure on the ground. The land under the Belle Époque wonder that is the Palais Garnier is stabilized by a man-made underground lake. Modern architects have also made their mark, mostly on the city’s museums, be it the inside-out structure of the Centre Pompidou or the dilating windows at the Institute du Monde Arabe.