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

From the Romanesque period on, most churches consist either of 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, it's called 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 the apse.

Some churches, especially after the Renaissance when mathematical proportion became important, were built on a Greek Cross plan, with each axis the same length, like a giant "+" (plus sign). By the baroque period, funky shapes became popular, with churches built in the round or as ellipses.

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

Classical: Greeks & Romans (6th Century B.C. to 4th Century A.D.)

The Greeks settled Sicily and southern Italy, and left behind some of the best-preserved ancient temples in the world.

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). The Romans then added the load-bearing arch. Roman builders were inventive engineers, developing hoisting mechanisms and a specially trained workforce.

Identifiable classical architectural features include these:

  • Classical orders. These were usually simplified into types of column capitals, with the least ornate used on a building's ground level and the most ornate used on the top: Doric (a plain capital), Ionic (a capital with a scroll), and Corinthian (a capital with flowering acanthus leaves).
  • Brick and concrete. Although marble is traditionally associated with Roman architecture, Roman engineers could also do wonders with bricks or even prosaic concrete -- concrete seating made possible such enormous theaters as Rome's 2.4-hectare (6-acre), 45,000-seat Colosseum.

Most Greek Temples in the Magna Graecia of southern Italy were built in the 5th-century-B.C. Doric style, including those at Paestum south of Naples, and in Sicily at Segesta and Agrigento, including the remarkably preserved Temple of Concord. Greek theaters survive in Sicily at Taormina, Segesta, and Syracuse (which was the largest in the ancient world).

One of the best places to see Roman architecture, of course, is Rome itself, where examples of most major public buildings still exist. These include the sports stadium of the Colosseum (1st c. A.D.), which perfectly displays the use of the Classical orders; Hadrian's marvel of engineering, the Pantheon (1st c. A.D.); the brick public Baths of Caracalla (3rd c. A.D.); and the Basilica of Constantine and Maxentius in the Roman Forum (4th c. A.D.). By the way, Roman basilicas, which served as law courts, took the form of rectangles supported by arches atop columns along both sides of the interior, with an apse at one or both ends; the form was later adopted by early Christians for their first grand churches.

Three Roman cities have been preserved, with their street plans and, in some cases, even buildings remaining intact. These are famous, doomed Pompeii and its neighbor Herculaneum (both buried by Vesuvius's A.D.-79 eruption), as well as Rome's ancient seaport Ostia Antica.

Romanesque (A.D. 800 to 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 accommodate the masses, who came to hear the priests say Mass but mainly to worship at the altars of various saints. To support the weight of all that masonry, walls had to be thick and solid (meaning they could be pierced only by few and rather small windows), resting on huge piers, giving churches a dark, somber, mysterious, and often oppressive feeling.

Identifiable Romanesque features include:

  • Rounded arches. These load-bearing architectural devices allowed 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.
  • Thick walls.
  • Infrequent and small windows.
  • Huge piers.
  • Blind arcades. A range of arches was carried on piers or columns and attached to a wall. Set into each arch's curve was often a lozenge, a diamond-shaped decoration, sometimes inlaid with colored marbles.
  • Stripes. Created by alternating layers of white and light-gray stones, this banding was typical of the Pisan-Romanesque style prominent in Pisa and Lucca. The gray got darker as time went on; by the late Romanesque/early Gothic period, the pattern often became a zebra of black and white stripes.
  • Stacked facade arcades. Another typical Pisan-Romanesque feature was a tall facade created by stacking small, open-air loggias with columns of different styles on top of one another to a height of three to five levels.

Modena's Duomo (12th c.) marks one of the earliest appearances of rounded arches, and its facade is covered with great Romanesque reliefs. Abbazia di Sant'Antimo (1118), outside Montalcino, is a beautiful example of French Romanesque style. Milan's Basilica di San Ambrogio (11th-12th c.) is festooned with the tiered loggias and arcades that became hallmarks of the Lombard Romanesque.

Pisa's Cathedral group (1153-1360s) is typical of the Pisan-Romanesque style, with stacked arcades of mismatched columns in the cathedral's facade (and wrapping around the famous Leaning Tower of Pisa) and blind arcading set with lozenges. Lucca's Cattedrale di San Martino and San Michele in Foro (11th-14th c.) are two more prime examples of the style.

Gothic (Late 12th to early 15th centuries)

By the late 12th century, engineering developments freed architecture from the heavy, thick walls of the Romanesque and allowed ceilings to soar, walls to thin, and windows to proliferate.

In place of the dark, somber, relatively unadorned Romanesque interiors that forced the eyes of the faithful toward the altar, where the priest stood droning on in unintelligible Latin, the Gothic interior enticed the churchgoers' gaze upward to high ceilings filled with light. The priests still conducted Mass in Latin, but now peasants could "read" the Gothic comic books of stained-glass windows.

The style began in France and was popular in Italy only in the northern region. From Florence south, most Gothic churches were built by the preaching orders of friars (Franciscans and Dominicans) as cavernous, barnlike structures.

Identifiable features of the French Gothic include:

  • Pointed arches. The most significant development of the Gothic era was the discovery that pointed arches could carry far more weight than rounded ones.
  • Cross vaults. Instead of being flat, the square patch of ceiling between four columns arches up to a point in the center, creating four sail shapes, sort of like the underside of a pyramid. The "X" separating these four sails is often reinforced with ridges called ribbing. As the Gothic progressed, four-sided cross vaults became six-sided, eight-sided, or multisided as architects played with the angles.
  • Tracery. These lacy spider webs of carved stone grace the pointy ends of windows and sometimes the spans of ceiling vaults.
  • Flying buttresses. 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, which took the form of minispires or statues.
  • Stained glass. Because pointy arches can carry more weight than rounded ones, windows could be larger and more numerous. They were often filled with Bible stories and symbolism written in the colorful patterns of stained glass.

The only truly French-style Gothic church in Italy is Milan's massive Duomo & Baptistry (begun ca. 1386), a lacy festival of pinnacles, buttresses, and pointy arches. Siena's Duomo (1136-1382), though started in the late Romanesque, has enough Giovanni Pisano sculptures and pointy arches to be considered Gothic. Florence has two of those barnlike Gothic churches: Basilica di Santa Maria Novella (1279-1357) and Basilica di Santa Croce (1294). The decorations inside Santa Maria Sopra Minerva (1280-1370), Rome's only Gothic church, are all of a later date, but the architecture itself is all pointy arches and soaring ceilings (though, hemmed in by other buildings, its interior is much darker than most Gothic places).

Renaissance (15th to 17th centuries)

As in painting, Renaissance architectural rules stressed proportion, order, classical inspiration, and mathematical precision to create unified, balanced structures. It was probably an 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.

Some identifiable Renaissance features include:

  • A sense of proportion
  • A reliance on symmetry
  • The use of classical orders

One of the first great Renaissance architects was Florence's Filippo Brunelleschi (1377-1476). He often worked in the simple scheme of soft white plaster walls with architectural details and lines in pale gray pietra serena stone. Among his masterpieces in Florence are the Basilica di Santa Croce's Pazzi Chapel (1442-46), decorated with Donatello roundels; the interior of the Basilica di San Lorenzo (1425-46); and, most famous, the ingenious dome capping Il Duomo (1420-46). This last truly exemplifies the Renaissance's debt to the ancients. Brunelleschi traveled to Rome and studied the Pantheon up close to unlock the engineering secrets of its vast dome to build his own.

Urbino architect Bramante (1444-1514) was perhaps the most mathematical and classically precise of the early High Renaissance architects, evident in his (much-altered) plans for Rome's St. Peter's Basilica (his spiral staircase in the Vatican Museums has survived untouched). Also see his jewel of perfect Renaissance architecture, the textbook Tempietto (1502) at San Pietro in Montorio on the slopes of Rome's Gianicolo Hill, where church officials once thought that St. Peter had been crucified (as a plus, the little crypt inside is a riotous rococo grotto).

Renaissance man Michelangelo (1475-1564) took up architecture late in life, designing Florence's Medici Laurentian Library (1524) and New Sacristy (1524-34), which houses the Medici Tombs at Basilica di San Lorenzo. In Rome, you can see his facade of the Palazzo Farnese (1566) and one of his crowning glories, the soaring dome of St. Peter's Basilica, among other structures.

The fourth great High Renaissance architect was Andrea Palladio (1508-80), who worked in a much more strictly classical mode of columns, porticoes, pediments, and other ancient temple-inspired features. His masterpieces include Villa Foscari and the great Villa Rotonda, both in the Veneto countryside around Vicenza. His final work is Vicenza's Olympic Theater (1580), an attempt to reconstruct a Roman theater stage as described in ancient writings. Other designs include the Venetian church San Giorgio Maggiore (1565-1610). He had great influence on architecture abroad as well; his "Palladian" style informed everything from British architecture to Thomas Jefferson's Monticello.

Baroque & Rococo (17th to 18th Centuries)

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, with 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). Excessively complex and dripping with decorative tidbits, rococo is kind of a twisted version of the baroque.

Some identifiable baroque features include:

  • Classical architecture rewritten with curves. The baroque is similar to Renaissance, but many of the right angles and ruler-straight lines are exchanged for curves of complex geometry and an interplay of concave and convex surfaces. 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.
  • Complex decoration. Unlike the sometimes severe and austere designs of the Renaissance, the baroque was playful. Architects festooned exteriors and encrusted interiors with an excess of decorations intended to liven things up -- lots of ornate stucco work, pouty cherubs, airy frescoes, heavy gilding, twisting columns, multicolored marbles, and general frippery.
  • Multiplying forms. Why use 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 that 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.

The baroque flourished across Italy. Though relatively sedate, Carlo Maderno's facade and Bernini's sweeping elliptical colonnade for Rome's St. Peter's Square make one of Italy's most famous baroque assemblages. One of the quirkiest and most felicitous baroque styles flourished in the churches of the Apulian city Lecce. When an earthquake decimated the Sicilian town of Noto near Syracuse, it was rebuilt from scratch on a complete baroque city plan; the streets and squares made viewing platforms for the theatrical backdrops of its churches and palaces.

For the rococo -- more a decorative than architectural movement -- look no further than Rome's Spanish Steps (1726), by architect de Sanctis, or the Trevi Fountain (1762), by Salvi.

Neoclassical to Modern (18th to 21st Centuries)

As a backlash against the excesses of the baroque and rococo, architects began turning to the austere simplicity and grandeur of the classical age and inaugurated the neoclassical style by the middle of the 18th century. Their work was inspired by the rediscovery of Pompeii and other ancient sites.

In the late 19th and 20th centuries, Italy's architectural styles went in several directions. The Industrial Age of the 19th century brought with it the first genteel shopping malls of glass and steel. The country's take on the early-20th-century Art Nouveau movement was called Liberty Style. Mussolini made a spirited attempt to bring back ancient Rome in what can only be called Fascist architecture. Since then, Italy has built mostly concrete and glass skyscrapers, like the rest of the world, although a few architects in the medium have stood out.

Some identifiable features of each of these movements include:

  • Neoclassical. The classical ideals of mathematical proportion and symmetry, first rediscovered during the Renaissance, are the hallmark of every classically styled era. Neoclassicists reinterpreted ancient temples as buildings and as decorative, massive colonnaded porticos.
  • Liberty Style. Like Art Nouveau practitioners in other countries, Italian decorators rebelled against the era of mass production by stressing the uniqueness of craft. They created asymmetrical, curvaceous designs based on organic inspiration (plants and flowers), and they used such materials as wrought iron, stained glass, tile, and hand-painted wallpaper.
  • Fascist. Deco meets Caesar. This period produced monumentally imposing and chillingly stark, white marble structures surrounded by statuary in the classical style.

Of the neoclassical, Caserta's Royal Palace (1752-74), outside Naples, was a conscious attempt to create a Versailles for the Bourbon monarchs, while the unbelievably huge (and almost universally derided) Vittorio Emanuele Monument (1884-1927) in Rome, which has been compared to a wedding cake or a Victorian typewriter, was Italy's main monument to reaching its Risorgimento goal of a unified Italy.

The Industrial Age created glass-domed shopping arcades in giant "X" shapes in both Milan and Naples. Liberty style never produced any surpassingly important buildings, although you can glimpse it occasionally in period storefronts.

Fascist architecture still infests corners of Italy (although most of the right-wing reliefs and the repeated engravings of DVCE -- Mussolini's nickname for himself -- have long since been chipped out). You can see it at its best in Rome's planned satellite community called EUR, which includes a multistory "square Colosseum" so funky that it has been featured in many a film and music video, and in Rome's Stadio Olimpico complex.

The mid-20th century was dominated by Pier Luigi Nervi (1891-1979) and his reinforced concrete buildings, Florence's Giovanni Berta Stadium (1932), Rome's Palazzeto dello Sport stadium (1960), and Turin's Exposition Hall (1949).

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