While each architectural era has its distinctive features, there are some elements, general floor plans, and terms common to many. Also, some features may appear near the end of one era and continue through several later ones.

From the Romanesque period on, most churches consist of either a single, wide aisle or a wide central nave flanked by two narrow aisles. The aisles are separated from the nave by a row of columns, or by square stacks of masonry called piers, usually connected by arches.

This main nave/aisle assemblage is usually crossed by a perpendicular corridor called a transept near the far, east end of the church so that the floor plan looks like a Latin Cross (shaped like a crucifix). The shorter, east arm of the nave is the holiest area, called the chancel; it often houses the stalls of the choir and the altar. If the far end of the chancel is rounded off, we call it an apse. An ambulatory is a curving corridor outside the altar and choir area, separating it from the ring of smaller chapels radiating off the chancel and apse.

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Some churches, especially after the Renaissance, when mathematical proportion became important, were built on a Greek cross plan, each axis the same length. By the baroque period, funky shapes became popular, with churches built in the round, or as ellipses, and so forth.

It's worth pointing out that very few buildings (especially churches) were built in only one particular style. These massive, expensive structures often took centuries to complete, during which time tastes would change and plans would be altered.

Ancient Rome (1st c. B.C.-4th c. A.D.)

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The Romans made use of certain Greek innovations, particularly architectural ideas. The first to be adopted was post-and-lintel construction -- essentially, a weight-bearing frame, like a door. Later came adaptation of Greek columns for supporting buildings, following the classical orders of Doric column capitals (the plain ones) on the ground floor, Ionic capitals (with the scrolls on either end) on the next level, and Corinthian capitals (flowering with acanthus leaves) on the top.

Romans thrived on huge complex problems for which they could produce organized, well-crafted solutions. Roman builders became inventive engineers, developing hoisting mechanisms and a specially trained workforce. They designed towns, built civic centers, raised grand temples and public baths, and developed the basilica, a rectangle supported by arches atop columns along both sides of the interior and with an apse at one or both ends. Basilicas were used for courts of justice, banking, and other commercial structures. The design was repeated all over the Roman world, beginning around the 1st century A.D. Later, early Christians adapted the architectural style for the first grand churches, still called basilicas.

Although marble is traditionally associated with Roman architecture, Roman engineers could also do wonders with bricks or even prosaic concrete. Their urban planning still stamps the street layouts of cities from Aosta (which preserves a gate and theater stage) to Brescia (with an ancient temple and theater remaining in the city center) to Verona (which preserves a magnificent ancient amphitheater still used for performances).

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Romanesque (A.D. 800-1300)

The Romanesque took its inspiration and rounded arches from ancient Rome (hence the name). Romanesque architects concentrated on building large churches with wide aisles to fit the ranks of people who came not only to hear the priests say Mass but mainly to worship at the altars of various saints. To support the weight of all that masonry, though, the walls had to be thick and solid (meaning they could be pierced only by few and rather small windows) resting on huge piers, giving Romanesque churches a dark, somber, mysterious, and often oppressive feeling.

The most identifiable Romanesque feature is rounded arches. These load-bearing architectural devices allowed the architects to open up wide naves and spaces, channeling all the weight of the stone walls and ceiling across the curve of the arch and down into the ground via the columns or pilasters. The style also made use of blind arcades, decorative bands of "filled-in" arches, the columns engaged in the wall and the arches' curves on top protruding mere inches. Set into each arch's curve is often a lozenge, a diamond-shaped decoration, typically inlaid with colored marbles.

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The Basilica of Sant'Ambrogio in Milan (11th-12th c.) is festooned with the tiered loggias and arcades that would become hallmarks of the Lombard Romanesque.

Gothic (Late 12th to Early 15th c.)

By the late 12th century, engineering developments -- most significantly the pointed arch, which could bear a much heavier load than a rounded one -- freed architects from the heavy, thick walls of Romanesque structures and allowed ceilings to soar, walls to thin, and windows to proliferate.

Instead of dark, somber, relatively unadorned Romanesque interiors that forced the eyes of the faithful toward the altar and its priest droning on in unintelligible Latin, the Gothic churchgoer's gaze was drawn up to high ceilings filled with light, a window unto heaven. The priests still gibbered in a dead language, but now peasants could "read" the Gothic comic books of colorful frescoes lining the walls and panels in stained-glass windows.

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In addition to those pointy arches, another Gothic innovation was the famous flying buttress. These free-standing exterior pillars connected by graceful, thin arms of stone help channel the weight of the building and its roof out and down into the ground. To help counter the cross-forces involved in this engineering sleight of hand, the piers of buttresses were often topped by heavy pinnacles or statues. Inside, the general pointiness continued with cross-vaults: The square patch of ceiling between four columns, instead of being flat, would arch up to a point in the center, creating four sail shapes, sort of like the underside of a pyramid with bulging faces. The X separating these four "sails" was often reinforced with ridges called ribbing. As the Gothic style progressed, four-sided cross-vaults became six-, eight-, or multisided as architects played with the angles they could make. In addition, tracery -- delicate, lacy spider webs of carved-stone curlicues -- graced the pointy end of windows and just about any acute angle throughout the architecture.

The true, French-style Gothic flourished only in northern Italy, and the best example is Milan's massive cathedral (Duomo), a festival of pinnacles, buttresses, and pointy arches begun in the late 14th century. Venice's I Frari is a bit airier and boxier; Padua's Basilica di Sant'Antonio is largely Gothic, though its Romanesque facade and Byzantine domes throw you off. In palace architecture, the Venetians developed a distinctive style of insetting lacy, lithe, pointed marble windows with an Eastern flair into pale pastel plaster walls. This is seen in countless palaces across Venice, especially in its most lavish: Ca' d'Oro, Ca' Foscari, and the model against which all were measured, the Palazzo Ducale itself.

Renaissance (15th-17th c.)

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As in painting, Renaissance architectural rules stressed proportion, order, classical inspiration, and mathematical precision to create unified, balanced structures. It was probably a Florentine architect, Filippo Brunelleschi, in the early 1400s, who first truly grasped the concept of "perspective" and provided artists with ground rules for creating the illusion of three dimensions on a flat surface.

The early Renaissance was truly codified by central Italian architects working in Florence and Rome, though influential early Florentine theorist Leon Battista Alberti (1404-72) built structures across Italy, including Sant'Andrea in Mantua. Urbino-born Donato Bramante (1444-1514), who would find fame in Rome building St. Peter's, got his start in Milan by converting the older church of San Satiro and rebuilding the altar end of Santa Maria delle Grazie.

The undisputed master of the High Renaissance was Andrea Palladio (1508-80), from the Veneto, who worked in a much more strictly classical mode of columns, porticoes, pediments, and other ancient temple-inspired features. In Venice, Jacopo Sansovino (1486-1570) reigned supreme, his loggia and Libreria Sansoviniana lining St. Mark's Square becoming a cornerstone of the High Renaissance, to be copied and repeated in such far-flung architectural endeavors as the cast-iron facades in New York's SoHo district.

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Raphael protégé Giulio Romano (1492-1546) designed Mantua's impressive Palazzo Te; Galeazzo Alessi (1512-72) was the premier architect of Genoa's famed palaces, many of which are now museums.

Andrea Palladio -- Father of Neoclassicism -- Order, balance, elegance, harmony with the landscape, and a human scale are all apparent in the creations of architect Andrea Palladio (1508-80). Palladio was working as a stonemason and sculptor when, at 30, inspired by the design of ancient buildings he studied on trips to Rome, he turned his hand to architecture and applied the principles of classical proportion to Renaissance ideals of grace, symmetry, and functionality. Vicenza, the little city near Venice where Palladio lived as a boy and where he returned in his prime, is graced with many Palladian palazzi and a church as well as his Teatro Olimpico. In Venice he designed the churches of San Giorgio Maggiore and Redentore.

Palladio is best known, though, for the villas he built on the flat plains of the Veneto for Venetian nobles yearning to escape the cramped city. Nineteen of these villas still stand, including what may be his finest, La Rotunda, outside Vicenza. The design of this and Palladio's other villas -- square, perfectly proportioned, elegant yet functional -- may strike a note of familiarity with American and British visitors: Palladio influenced generations of architects who followed his lead when they designed neoclassical plantation houses in the American South and country estates in England, his "Palladian" style informing everything from British architecture to Thomas Jefferson's Monticello.

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Other Palladio masterpieces include Vicenza's Palazzo della Ragione and Palazzo Valmarana (1566), and, in the Veneto countryside around Vicenza, the Villa Babaro and Villa Foscari. His final work is the Teatro Olimpico, in Vicenza (1580), an attempt to reconstruct a Roman theater stage backdrop as described in ancient writings. He also designed the Venetian churches San Giorgio Maggiore (1565-1610) and Il Redentore.

Baroque & Rococo (17th-18th c.)

More than any other movement, the baroque aimed toward a seamless meshing of architecture and art. The stuccoes, sculptures, and paintings were all carefully designed to complement each other -- and the space itself -- to create a unified whole. This whole was both aesthetic and narrative, the various art forms all working together to tell a single biblical story (or often to subtly relate the deeds of the commissioning patron to great historic or biblical events).

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In the baroque, classical architecture exchanges its crisp angles and ruler-straight lines for curves of complex geometry and an interplay of concave and convex. The overall effect is to lighten the appearance of structures and add movement of line and vibrancy to the static look of the classical Renaissance.

Unlike the sometimes severe and austere designs of the Renaissance, the baroque was playful. Architects festooned structures and encrusted interiors with an excess of decorations intended to liven things up -- lots of ornate stuccowork, pouty cherubs, airy frescoes, heavy gilding, twisting columns, multicolored marbles, and general frippery.

The baroque was also a movement of multiplying forms. The baroque asked, why make do with one column when you can stack a half-dozen partial columns on top of each other, slightly offset, until the effect is like looking at a single column though a fractured kaleidoscope? The baroque loved to pile up its forms and elements to create a rich, busy effect, breaking a pediment curve into segments so each would protrude farther out than the last, or building up an architectural feature by stacking short sections of concave walls, each one curving to a different arc.

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Rococo is the baroque gone awry into the grotesque, excessively complex and dripping with decorative tidbits.

The baroque flourished across Italy, but frankly, little of it was truly inspired architecture. You'll find good examples in Venice's Santa Maria della Salute, and especially in Turin, from the Castellamonte-designed Piazza San Carlo to the great works of Guarino Guarini (San Lorenzo, Palazzo Carignano, the San Sidone chapel for the Holy Shroud in the cathedral) and Filippo Juvarra (Basilica di Superga, Palazzina di Stupinigi).

Neoclassical to Modern (18th-21st c.)

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By the middle of the 18th century, as a backlash against the excesses of the baroque and rococo, architects, inspired by the rediscovery of Pompeii and other ancient sites, began turning to the austere simplicity and grandeur of the classical age and inaugurated a neoclassical style. The classical ideals of mathematical proportion and symmetry, first rediscovered during the Renaissance, are the hallmark of every classically styled era -- a reinterpretation of ancient temples into buildings and massive colonnaded porticos. Northern Italy's two famed opera houses are both excellent neoclassical exercises: Milan's La Scala and Venice's La Fenice. To see perhaps the best example of the chilliness the neoclassical style often entailed, pop into Padua's Caffè Pedrocchi for a cappuccino (interestingly, the architect, Giuseppe Japelli -- who also worked in rococo and Palladian idioms -- drew inspiration not just from classical Greece/Rome but also ancient Egypt).

Italy's take on the early-20th-century Art Nouveau movements was called Liberty. Like all Art Nouveau, decorators rebelling against the era of mass production stressed a craft of uniqueness, creating asymmetrical, curvaceous designs based on organic inspiration (plants and flowers) and using wrought iron, stained glass, tile, and hand-painted wallpaper.

The Industrial Age of the late 19th/early 20th centuries brought with it the first genteel shopping malls of glass and steel girders, such as the famed Galleria in Milan. Mussolini made a spirited attempt to bring back ancient Rome in what can only be called Fascist architecture: Deco meets Caesar. Monumentally imposing and chillingly stark white marble structures are surrounded by classical-style statues. Fascist architecture still infests all corners of Italy, though most of the right-wing reliefs and the repeated engravings of "DVCE" -- Mussolini's nickname for himself -- have long since been chipped out. One of the best, easily accessible, oft-overlooked examples is Milan's massive train station (so if you're stuck with a long wait, wander outside to squint up at the weird Deco gargoyles and call your layover sightseeing).

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Fitting into no style is Turin's truly odd Mole Antonellina (1863-97), designed as a synagogue but later put to various uses (currently, it is a film museum). Its squat brick base is topped by a steep cone supporting several layers of Greek temples piled one atop the other at right angles, capped off in turn by a needlelike spire at 166m (544 ft.).

Since then, Italy has mostly poured concrete and glass skyscrapers like the rest of us, though a few architects in the medium have stood out. The mid-20th century was dominated by Pier Luigi Nervi (1891-1979) and his reinforced concrete buildings, including Turin's Exposition Hall (1949). Italy's greatest living architect, Pritzker Prize-winning Renzo Piano (b. 1937), lives in Paris, and most of his great commissions, including the Pompidou, are outside of Italy.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.