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Ancient Roman architecture developed different aspects of Ancient Greek architecture and newer technologies such as the arch and the dome to create a new architectural style. Roman architecture flourished throughout the Empire during the Pax Romana. Its use of new materials, particularly concrete, was an important feature.
Roman Architecture covers the period from the establishment of the Roman Republic in 509 BC to about the 4th century AD, after which it becomes reclassified as Late Antique or Byzantine architecture. Most of the many surviving examples are from the later imperial period. Roman architectural style continued to influence building in the former empire for many centuries, and the style used in Western Europe beginning about 1000 is called Romanesque architecture to reflect this dependence on basic Roman forms.
The Ancient Romans were responsible for significant developments in housing and public hygiene, for example their public and private baths and latrines, under-floor heating in the form of the hypocaust, mica glazing (examples in Ostia Antica), and piped hot and cold water (examples in Pompeii and Ostia).
Factors such as wealth and high population densities in cities forced the ancient Romans to discover new architectural solutions of their own. The use of vaults and arches, together with a sound knowledge of building materials, enabled them to achieve unprecedented successes in the construction of imposing structures for public use. Examples include the aqueducts of Rome, the Baths of Diocletian and the Baths of Caracalla, the basilicas and Colosseum. These were reproduced at smaller scale in most important towns and cities in the Empire. Some surviving structures are almost complete, such as the town walls of Lugo in Hispania Tarraconensis, now northern Spain.
The Ancient Romans intended that public buildings should be made to impress, as well as perform a public function. The Romans did not feel restricted by Greek aesthetic axioms alone in achieving these objectives. The Pantheon is an example of this,particularly in the version rebuilt by Hadrian,which remains perfectly preserved, and which were over the centuries that has served, particularly in the Western Hemisphere,as the inspiration for countless public buildings. The same emperor left his mark on the landscape of northern Britain when he built a wall to mark the limits of the empire, and after further conquests in Scotland, the Antonine Wall was built to replace Hadrian's Wall.
The Romans were indebted to their Etruscan neighbors and forefathers who supplied them with a wealth of knowledge essential for future architectural solutions, such as the use of hydraulics and the construction of arches. The Romans absorbed Greek Architectural influence both directly (e.g. Magna Graecia) and indirectly (e.g. Etruscan Architecture was itself influenced by the Greeks). The influence is evident in many ways; for example, in the introduction and use of the Triclinium in Roman villas as a place and manner of dining. The Romans were also known to employ Greek craftsmen and engineers to construct Roman buildings.
The Roman Architectural Revolution, also known as the Concrete Revolution, was the widespread use in Roman architecture of the previously little-used architectural forms of the arch, vault, and dome. For the first time in history, their potential was fully exploited in the construction of a wide range of civil engineering structures, public buildings, and military facilities. These included amphitheatres, aqueducts, baths, bridges, circuses, dams, domes, harbours, and temples.
A crucial factor in this development, which saw a trend toward monumental architecture, was the invention of Roman concrete (opus caementicium), which led to the liberation of shapes from the dictates of the traditional materials of stone and brick.
The Roman use of the arch and their improvements in the use of concrete and bricks facilitated the building of the many aqueducts throughout the empire, such as the Aqueduct of Segovia and the eleven aqueducts in Rome itself, including the Aqua Claudia and Anio Novus. The same concepts produced numerous bridges, some of which are still in daily use, for example the Puente Romano at Mérida in Spain, and the Pont Julien and the bridge at Vaison-la-Romaine, both in Provence, France.
The dome permitted construction of vaulted ceilings without crossbeams and made possible large covered public space such as public baths and basilicas. The Romans based much of their architecture on the dome, such as Hadrian's Pantheon in the city of Rome, the Baths of Diocletian and the Baths of Caracalla.
The use of arches that spring directly from the tops of columns was a Roman development, seen from the 1st century AD, that was very widely adopted in medieval Western, Byzantine and Islamic architecture.
Art historians such as Gottfried Richter in the 1920s have identified the most important Roman architectural innovation as the Triumphal Arch. This symbol of power was transformed and utilised within the Christian basilicas when the Roman Empire of the West was on its last legs. The arch was set before the altar to symbolize the triumph of Christ and the afterlife. The arch is seen in aqueducts, especially in the many surviving examples, such as the Pont du Gard, the aqueduct at Segovia and the remains of the Aqueducts of Rome itself. Their survival is testimony to the durability of their materials and design.
The Romans first adopted the arch from the Etruscans, and implemented it in their own building. An arch transmits load evenly and is still commonly used in architecture today.
On his return from campaigns in Greece, the general Sulla brought back what is probably the most well-known element of the early imperial period, the mosaic, a decoration made of colourful chips of stone inserted into cement. This tiling method took the empire by storm in the late first century and the second century and in the Roman home joined the well known mural in decorating floors, walls, and grottoes with geometric and pictorial designs.
There were two main techniques in Greco-Roman mosaic: opus vermiculatum used tiny tesserae, typically cubes of 4 millimeters or less, and was produced in workshops in relatively small panels which were transported to the site glued to some temporary support. The tiny tesserae allowed very fine detail, and an approach to the illusionism of painting. Often small panels called emblemata were inserted into walls or as the highlights of larger floor-mosaics in coarser work. The normal technique, however, was opus tessellatum, using larger tesserae, which were laid on site. There was a distinct native Italian style using black on a white background, which was no doubt cheaper than fully coloured work.
A specific genre of Roman mosaic obtained the name asaroton (Greek "unswept floor"). It represented an optical illusion of the leftovers from a feast on the floor of reach houses.
A hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. The Roman architect Vitruvius, writing about the end of the 1st century B.C., attributes their invention to Sergius Orata. Many remains of Roman hypocausts have survived throughout Europe, western Asia, and northern Africa. The hypocaust was an invention which improved the hygiene and living conditions of citizens, and was a forerunner of modern central heating.
Hypocausts were used for heating hot baths (thermae), houses and other buildings, whether public or private. The floor was raised above the ground by pillars, called pilae stacks, with a layer of tiles, then a layer of concrete, then another of tiles on top; and spaces were left inside the walls so that hot air and smoke from the furnace would pass through these enclosed areas and out of flues in the roof, thereby heating but not polluting the interior of the room.
In Sicily truss roofs presumably appeared as early as 550 BC.Their potential was fully realized in the Roman period, which saw trussed roofs over 30 wide spanning the rectangular spaces of monumental public buildings such as temples, basilicas, and later churches. Such spans were thrice as wide as the widest prop-and-lintel roofs and only surpassed by the largest Roman domes.
The largest truss roof by span of Ancient Rome covered the Aula Regia (throne room) built for emperor Domitian (81–96 AD) on the Palatine Hill, Rome. The timber truss roof had a width of 31.67 m, slightly surpassing the postulated limit of 30 m for Roman roof constructions. Tie-beam trusses allowed for much larger spans than the older prop-and-lintel system and even concrete vaulting. Nine out of the ten largest rectangular spaces in Roman architecture were bridged this way, the only exception being the groin vaulted Basilica of Maxentius.
The spiral stair is a type of stairway which, due to its complex helical structure, was introduced relatively late into architecture. Although the oldest example dates back to the 5th century BC, it was only in the wake of the influential design of Trajan's Column that this space-saving new type permanently caught hold in Roman architecture.
Apart from the triumphal columns in the imperial cities of Rome and Constantinople, other types of buildings such as temples, thermae, basilicas and tombs were also fitted with spiral stairways. Their notable absence in the towers of the Aurelian Wall indicates that although used in medieval castles, they did not yet figure prominently in Roman military engineering. By late antiquity, separate stair towers were constructed adjacent to the main buildings, as in the Basilica of San Vitale.
Roman influences may be found around us today, in banks, government buildings, great houses, and even small houses, perhaps in the form of a porch with Doric columns and a pediment or in a fireplace or a mosaic shower floor copied from an original in Pompeii or Herculaneum. The mighty pillars, domes and arches of Rome echo in the New World too, where in Washington DC we see them in the Capitol Building, the White House, the Lincoln Memorial and other government buildings. All across the US the seats of regional government were normally built in the grand traditions of Rome, with vast flights of stone steps sweeping up to towering pillared porticoes, with huge domes gilded or decorated inside with the same or similar themes that were popular in Rome.
In wealthy provincial parts of the US such as the great plantations of 18th and 19th century Louisiana, there too are the pillars and porticoes, the symmetrical façades with their pilasters, the domes and statuary that would have seemed familiar to Caesar and Augustus.
In Britain, a similar enthusiasm has seen the construction of thousands of neo-Classical buildings over the last five centuries, both civic and domestic, and many of the grandest country houses and mansions are purely Classical in style, an obvious example being Buckingham Palace.
Tile covered concrete quickly supplanted marble as the primary building material, and more daring buildings soon followed, with great pillars supporting broad arches and domes rather than dense lines of columns suspending flat architraves. The freedom of concrete also inspired the colonnade screen, a row of purely decorative columns in front of a load-bearing wall. In smaller-scale architecture, concrete's strength freed the floor plan from rectangular cells to a more free-flowing environment. Most of these developments are described by Vitruvius, writing in the first century AD in his work De Architectura.
The Romans made fired clay bricks, and the Roman legions, which operated mobile kilns, introduced bricks to many parts of the empire. Roman bricks are often stamped with the mark of the legion that supervised their production. The use of bricks in southern and western Germany, for example, can be traced back to traditions already described by the Roman architect Vitruvius.
Roman brick was almost invariably of a lesser height than modern brick, but was made in a variety of different shapes and sizes. Shapes included square, rectangular, triangular and round, and the largest bricks found have measured over three feet in length. Ancient Roman bricks had a general size of 1½ Roman feet by 1 Roman foot, but common variations up to 15 inches existed. Other brick sizes in Ancient Rome included 24" x 12" x 4", and 15" x 8" x 10". Ancient Roman bricks found in France measured 8" x 8" x 3". The Constantine Basilica in Trier is constructed from Roman bricks 15" square by 1½" thick. There is often little obvious difference (particularly when only fragments survive) between Roman bricks used for walls on the one hand, and tiles used for roofing or flooring on the other, so archaeologists sometimes prefer to employ the generic term ceramic building material (or CBM).
The Romans perfected brick-making during the first century of their empire and used it ubiquitously, in public and private construction alike. The Romans took their brickmaking skills everywhere they went, introducing the craft to the local populations. In the British Isles, the introduction of Roman brick by the ancient Romans was followed by a 600–700 year gap in major brick production.
Although concrete had been used on a minor scale in Mesopotamia, Roman architects perfected Roman concrete and used it in buildings where it could stand on its own and support a great deal of weight. The first use of concrete by the Romans was in the town of Cosa sometime after 273 BC. Ancient Roman concrete was a mixture of lime mortar, sand with stone rubble, pozzolana, water, and stones, and stronger than previously-used concrete. The ancient builders placed these ingredients in wooden frames where they hardened and bonded to a facing of stones or (more frequently) bricks.
When the framework was removed, the new wall was very strong, with a rough surface of bricks or stones. This surface could be smoothed and faced with an attractive stucco or thin panels of marble or other coloured stones called revetment. Concrete construction proved to be more flexible and less costly than building solid stone buildings. The materials were readily available and not difficult to transport. The wooden frames could be used more than once, allowing builders to work quickly and efficiently.
Though most would consider concrete the Roman contribution most relevant to the modern world, the Empire's style of architecture can still be seen throughout Europe and North America in the arches and domes of many governmental and religious buildings.
The ancient Romans employed regular orthogonal structures on which they molded their colonies.  They probably were inspired by Greek and Hellenic examples, as well as by regularly planned cities that were built by the Etruscans in Italy. (see Marzabotto)
The Romans used a consolidated scheme for city planning, developed for military defense and civil convenience. The basic plan consisted of a central forum with city services, surrounded by a compact, rectilinear grid of streets, and wrapped in a wall for defense. To reduce travel times, two diagonal streets crossed the square grid, passing through the central square. A river usually flowed through the city, providing water, transport, and sewage disposal. Hundreds of towns and cities were built by the Romans throughout their empire. Many European towns, such as Turin, preserve the remains of these schemes, which show the very logical way the Romans designed their cities. They would lay out the streets at right angles, in the form of a square grid. All roads were equal in width and length, except for two, which were slightly wider than the others. One of these ran east–west, the other, north–south, and they intersected in the middle to form the center of the grid. All roads were made of carefully fitted flag stones and filled in with smaller, hard-packed rocks and pebbles. Bridges were constructed where needed. Each square marked off by four roads was called an insula, the Roman equivalent of a modern city block.
Each insula was 80 yards (73 m) square, with the land within it divided. As the city developed, each insula would eventually be filled with buildings of various shapes and sizes and crisscrossed with back roads and alleys. Most insulae were given to the first settlers of a Roman city, but each person had to pay to construct his own house.
The city was surrounded by a wall to protect it from invaders and to mark the city limits. Areas outside city limits were left open as farmland. At the end of each main road was a large gateway with watchtowers. A portcullis covered the opening when the city was under siege, and additional watchtowers were constructed along the city walls. An aqueduct was built outside the city walls.
The development of Greek and Roman urbanization is relatively well-known, as there are relatively many written sources, and there has been much attention to the subject, since the Romans and Greeks are generally regarded as the main ancestors of modern Western culture. It should not be forgotten, though, that there were also other cultures with more or less urban settlements in Europe, primarily of Celtic origin. Among these, there are also some that appear to have been newly planned, such as the Lusatian town of Biskupin in Poland.
Some of the most impressive secular buildings are the amphitheatres, over 220 being known and many of which are well preserved, such as that at Arles, as well as its progenitor, the Colosseum in Rome. They were used for gladiatorial contests, public displays, public meetings and bullfights, the tradition of which still survives in Spain. Their typical shape, functions and name distinguish them from Roman theatres, which are more or less semicircular in shape; from the circuses (akin to hippodromes) whose much longer circuits were designed mainly for horse or chariot racing events; and from the smaller stadia, which were primarily designed for athletics and footraces.
The earliest Roman amphitheatres date from the middle of the first century BC, but most were built under Imperial rule, from the Augustan period (27 BC–14 AD) onwards. Imperial amphitheatres were built throughout the Roman empire; the largest could accommodate 40,000–60,000 spectators, and the most elaborate featured multi-storeyed, arcaded façades and were elaborately decorated with marble, stucco and statuary. After the end of gladiatorial games in the 5th century and of animal killings in the sixth, most amphitheatres fell into disrepair, and their materials were mined or recycled. Some were razed, and others converted into fortifications. A few continued as convenient open meeting places; in some of these, churches were sited.
The Roman basilica was a large public building where business or legal matters could be transacted. The first basilicas had no religious function at all. As early as the time of Augustus, a public basilica for transacting business had been part of any settlement that considered itself a city, used in the same way as the late medieval covered market houses of northern Europe, where the meeting room, for lack of urban space, was set above the arcades, however. Although their form was variable, basilicas often contained interior colonnades that divided the space, giving aisles or arcaded spaces on one or both sides, with an apse at one end (or less often at each end), where the magistrates sat, often on a slightly raised dais. The central aisle tended to be wide and was higher than the flanking aisles, so that light could penetrate through the clerestory windows.
The oldest known basilica, the Basilica Porcia, was built in Rome in 184 BC by Cato the Elder during the time he was Censor. Other early examples include the basilica at Pompeii (late 2nd century BC).
The Roman circus was a large open-air venue used for public events in the ancient Roman Empire. The circuses were similar to the ancient Greek hippodromes, although circuses served varying purposes and differed in design and construction. Along with theatres and amphitheatres, Circuses were one of the main entertainment sites of the time. Circuses were venues for chariot races, horse races, and performances that commemorated important events of the empire were performed there. For events that involved re-enactments of naval battles, the circus was flooded with water.
The performance space of the Roman circus was normally, despite its name, an oblong rectangle of two linear sections of race track, separated by a median strip running along the length of about two thirds the track, joined at one end with a semicircular section and at the other end with an undivided section of track closed (in most cases) by a distinctive starting gate known as the carceres, thereby creating a circuit for the races.
The Romans were the first builders in the history of architecture to realize the potential of domes for the creation of large and well-defined interior spaces. Domes were introduced in a number of Roman building types such as temples, thermae, palaces, mausolea and later also churches. Half-domes also became a favoured architectural element and were adopted as apses in Christian sacred architecture.
Monumental domes began to appear in the 1st century BC in Rome and the provinces around the Mediterranean Sea. Along with vaults, they gradually replaced the traditional post and lintel construction which makes use of the column and architrave. The construction of domes was greatly facilitated by the invention of concrete, a process which has been termed the Roman Architectural Revolution. Their enormous dimensions remained unsurpassed until the introduction of structural steel frames in the late 19th century (see List of the world's largest domes).
A forum was a public square in a Roman municipium, or any civitas, reserved primarily for the vending of goods; i.e., a marketplace, along with the buildings used for shops and the stoas used for open stalls. Many forums were constructed at remote locations along a road by the magistrate responsible for the road, in which case the forum was the only settlement at the site and had its own name, such as Forum Popili or Forum Livi.
Every city had a forum of varying size. In addition to its standard function as a marketplace, a forum was a gathering place of great social significance, and often the scene of diverse activities, including political discussions and debates, rendezvous, meetings, etc. The best known example is probably in Rome, Italy, and is the site of the earliest forum of the empire.
In new Roman towns the Forum was usually located at, or just off, the intersection of the main north-south and east-west streets (the Cardo and Decumanus). All forums would have a Temple of Jupiter at the north end, and would also contain other temples, as well as the Basilica; a public weights and measures table, so customers at the market could ensure they were not being sold short measures; and would often have the baths nearby.
A horreum was a type of public warehouse used during the ancient Roman period. Although the Latin term is often used to refer to granaries, Roman horrea were used to store many other types of consumables; the giant Horrea Galbae in Rome were used not only to store grain but also olive oil, wine, foodstuffs, clothing and even marble. By the end of the imperial period, the city of Rome had nearly 300 horrea to supply its demands. The biggest were enormous, even by modern standards; the Horrea Galbae contained 140 rooms on the ground floor alone, covering an area of some 225,000 square feet (21,000 m²).
The first horrea were built in Rome towards the end of the 2nd century BC, with the first known public horreum being constructed by the ill-fated tribune Gaius Gracchus in 123 BC. The word came to be applied any place designated for the preservation of goods; thus it was often used refer to cellars (horrea subterranea), but it could also be applied to a place where artworks were stored, or even to a library. Some public horrea functioned somewhat like banks, where valuables could be stored, but the most important class of horrea were those where foodstuffs such as grain and olive oil were stored and distributed by the state.
Multi-story apartment blocks called insulae catered to a range of residential needs. The cheapest rooms were at the top owing to the inability to escape in the event of a fire and the lack of piped water. Windows were mostly small, facing the street, with iron security bars. Insulae were often dangerous, unhealthy, and prone to fires because of overcrowding and haphazard cooking arrangements. There are examples in the Roman port town of Ostia, that date back to the reign of Trajan. External walls were in "Opus Reticulatum" and interiors in "Opus Incertum", which would then be plastered and sometimes painted.
To lighten up the small dark rooms, tenants able to afford a degree of luxury painted colourful murals on the walls. Examples have been found of jungle scenes with wild animals and exotic plants. Imitation windows (trompe l'oeil) were sometimes painted to make the rooms seem less confined.
Ancient Rome is known to have had elaborated, massive and beautiful houses and buildings. These houses and buildings belonged to those in higher social status. The average house of a commoner or Plebe did not contain many luxuries. There were members of the upper class that attended to flash their wealth into their design and architecture of their house. Many Romans perceived this morally wrong and considered to be luxuria or vice to makes people squander their money (wealth).They showed more regard towards convenience than expense. Domus, or single-family residences, were rare, with most having a layout of the closed unit, consisting of one or two rooms. Between 312 to 315 A.D. Rome had from 1781 domus and 44,850 of insulae.
Insula has been the subject of great debate for historians of Roman culture, as they argued over the various meanings of the word. Insula was a word used to describe apartment buildings, or the apartments themselves, meaning apartment, or inhabitable room, demonstrating just how small apartments for Plebes were. Urban divisions were originally street blocks, and later began to divide into smaller divisions, the word insula referring to both blocks and smaller divisions. The insula contained cenacula, tabernae, storage rooms under the stairs, and lower floor shops. Another type of housing unit for Plebes was a cenaculum, an apartment, divided into three individual rooms: cubiculum, exedra, and medianum. Common Roman apartments were mainly masses of smaller and larger structures, many with narrow balconies that present mysteries as to their use, having no doors to access them, and they lacked the excessive decoration and display of wealth that aristocrats’ houses contained. Luxury in houses was not common, as the life of the average person did not consist of being in their houses, as they instead would go to public baths, and engage in other communal activities.
Many lighthouses were built around the Mediterranean and the coasts of the empire, including the Tower of Hercules at A Coruña in northern Spain, a structure which survives to this day. A smaller lighthouse at Dover, England also exists as a ruin about half the height of the original. The light would have been provided by a fire at the top of the structure.
All Roman cities had at least one Thermae, a popular facility for public bathing, exercising and socializing. Exercise might include wrestling and weight-lifting, as well as swimming. Bathing was an important part of the Roman day, where some hours might be spent, at a very low cost subsidized by the government. Wealthier Romans were often accompanied by one or more slaves, who performed any required tasks such as fetching refreshment, guarding valuables, providing towels, and at the end of the session, applying olive oil to their masters' bodies which was then scraped off with a strigil, a scraper made of wood or bone. Romans did not wash with soap and water as we do now.
Roman bath-houses were also provided for private villas, town houses and forts. They were normally supplied with water from an adjacent river or stream, or by aqueduct. The design of thermae is discussed by Vitruvius in De Architectura.
Roman architecture was often at its most beautiful and impressive when adapted to the needs of Roman religion. The Pantheon in Rome has survived structurally intact because it has been continuously used for worship since it was built, over 2000 years ago. Although its interiors were altered when worship changed from paganism to Christianity, it is the finest and largest example of a dome built in antiquity still surviving.
Roman theatres were built in all areas of the empire from medieval-day Spain, to the Middle East. Because of the Romans' ability to influence local architecture, we see numerous theatres around the world with uniquely Roman attributes.
These buildings were semi-circular and possessed certain inherent architectural structures, with minor differences depending on the region in which they were constructed. The scaenae frons was a high back wall of the stage floor, supported by columns. The proscaenium was a wall that supported the front edge of the stage with ornately decorated niches off to the sides. The Hellenistic influence is seen through the use of the proscaenium. The Roman theatre also had a podium, which sometimes supported the columns of the scaenae frons. The scaenae was originally not part of the building itself, constructed only to provide sufficient background for the actors. Eventually, it became a part of the edifice itself, made out of concrete. The theatre itself was divided into the stage (orchestra) and the seating section (auditorium). Vomitoria or entrances and exits were made available to the audience.
A Roman villa was a Roman country house built for the upper class during the Roman republic and the Roman Empire. The Empire contained many kinds of villas, not all of them lavishly appointed with mosaic floors and frescoes. In the provinces, any country house with some decorative features in the Roman style may be called a "villa" by modern scholars. Some were pleasure houses such as those— like Hadrian's Villa at Tivoli— that were sited in the cool hills within easy reach of Rome or— like the Villa of the Papyri at Herculaneum— on picturesque sites overlooking the Bay of Naples. Some villas were more like the country houses of England or Poland, the visible seat of power of a local magnate, such as the famous palace rediscovered at Fishbourne in Sussex.
Suburban villas on the edge of cities were also known, such as the Middle and Late Republican villas that encroached on the Campus Martius, at that time on the edge of Rome, and which can be also seen outside the city walls of Pompeii. These early suburban villas, such as the one at Rome's Auditorium site or at Grottarossa in Rome, demonstrate the antiquity and heritage of the villa suburbana in Central Italy. It is possible that these early, suburban villas were also in fact the seats of power (maybe even palaces) of regional strongmen or heads of important families (gentes).
A third type of villa provided the organizational center of the large holdings called latifundia, that produced and exported agricultural produce; such villas might be lacking in luxuries. By the 4th century, villa could simply connote an agricultural holding: Jerome translated the Gospel of Mark (xiv, 32) chorion, describing the olive grove of Gethsemane, with villa, without an inference that there were any dwellings there at all (Catholic Encyclopedia "Gethsemane").
The initial invention of the watermill appears to have occurred in the hellenized eastern Mediterranean in the wake of the conquests of Alexander the Great and the rise of Hellenistic science and technology. In the subsequent Roman era, the use of water-power was diversified and different types of watermills were introduced. These include all three variants of the vertical water wheel as well as the horizontal water wheel. Apart from its main use in grinding flour, water-power was also applied to pounding grain, crushing ore, sawing stones and possibly fulling and bellows for iron furnaces.
Roman roads were vital to the maintenance and development of the Roman state, and were built from about 500 BC through the expansion and consolidation of the Roman Republic and the Roman Empire. They provided efficient means for the overland movement of armies, officials and civilians, and the inland carriage of official communications and trade goods. At the peak of Rome's development, no fewer than 29 great military highways radiated from the capital, and the Late Empire's 113 provinces were interconnected by 372 great road links. Roman road builders aimed at a regulation width (see Laws and standards above), but actual widths have been measured at between 3.6 ft (1.1 m) and more than 23 ft (7.0 m). Today, the concrete has worn from the spaces around the stones, giving the impression of a very bumpy road, but the original practice was to produce a surface that was no doubt much closer to being flat.
The Romans constructed numerous aqueducts in order to bring water from distant sources into their cities and towns, supplying public baths, latrines, fountains and private households. Waste water was removed by complex sewage systems and released into nearby bodies of water, keeping the towns clean and free from effluent. Aqueducts also provided water for mining operations, milling, farms and gardens.
Aqueducts moved water through gravity alone, being constructed along a slight downward gradient within conduits of stone, brick or concrete. Most were buried beneath the ground, and followed its contours; obstructing peaks were circumvented or, less often, tunnelled through. Where valleys or lowlands intervened, the conduit was carried on bridgework, or its contents fed into high-pressure lead, ceramic or stone pipes and siphoned across. Most aqueduct systems included sedimentation tanks, sluices and distribution tanks to regulate the supply at need.
Rome's first aqueduct supplied a water-fountain sited at the city's cattle market. By the third century AD, the city had eleven aqueducts, sustaining a population of over a million in a water-extravagant economy; most of the water supplied the city's many public baths. Cities and municipalities throughout the Roman Empire emulated this model, and funded aqueducts as objects of public interest and civic pride, "an expensive yet necessary luxury to which all could, and did, aspire."
Most Roman aqueducts proved reliable, and durable; some were maintained into the early modern era, and a few are still partly in use. Methods of aqueduct surveying and construction are noted by Vitruvius in his work De Architectura (1st century BC). The general Frontinus gives more detail in his official report on the problems, uses and abuses of Imperial Rome's public water supply. Notable examples of aqueduct architecture include the supporting piers of the Aqueduct of Segovia, and the aqueduct-fed cisterns of Constantinople.
Roman bridges, built by ancient Romans, were the first large and lasting bridges built. Roman bridges were built with stone and had the arch as the basic structure (see arch bridge). Most utilized concrete as well, which the Romans were the first to use for bridges.
Roman arch bridges were usually semicircular, although a few were segmental (such as Alconétar Bridge). A segmental arch is an arch that is less than a semicircle. The advantages of the segmental arch bridge were that it allowed great amounts of flood water to pass under it, which would prevent the bridge from being swept away during floods and the bridge itself could be more lightweight. Generally, Roman bridges featured wedge-shaped primary arch stones (voussoirs) of the same in size and shape. The Romans built both single spans and lengthy multiple arch aqueducts, such as the Pont du Gard and Segovia Aqueduct. Their bridges featured from an early time onwards flood openings in the piers, e.g. in the Pons Fabricius in Rome (62 BC), one of the world's oldest major bridges still standing. Roman engineers were the first and until the industrial revolution the only ones to construct bridges with concrete, which they called Opus caementicium. The outside was usually covered with brick or ashlar, as in the Alcántara bridge.
The Romans also introduced segmental arch bridges into bridge construction. The 330 m long Limyra Bridge in southwestern Turkey features 26 segmental arches with an average span-to-rise ratio of 5.3:1, giving the bridge an unusually flat profile unsurpassed for more than a millennium. Trajan's bridge over the Danube featured open-spandrel segmental arches made of wood (standing on 40 m high concrete piers). This was to be the longest arch bridge for a thousand years both in terms of overall and individual span length, while the longest extant Roman bridge is the 790 m long Puente Romano at Mérida.
Roman canals were typically multi-purpose structures, intended for irrigation, drainage, land reclamation, flood control and navigation where feasible. Some navigational canals were recorded by ancient geographers and are still traceable by modern archaeology. Channels which served the needs of urban water supply are covered at the List of aqueducts in the Roman Empire.
Freshwater reservoirs were commonly set up at the termini of aqueducts and their branch lines, supplying urban households, agricultural estates, imperial palaces, thermae or naval bases of the Roman navy.
Roman dam construction began in earnest in the early imperial period. For the most part, it concentrated on the semi-arid fringe of the empire, namely the provinces of North Africa, the Near East, and Hispania.  The relative abundance of Spanish dams below is due partly to more intensive field work there; for Italy only the Subiaco Dams, created by emperor Nero (54–68 AD) for recreational purposes, are attested. These dams are noteworthy, though, for their extraordinary height, which remained unsurpassed anywhere in the world until the Late Middle Ages.
The most frequent dam types were earth- or rock-filled embankment dams and masonry gravity dams. These served a wide array of purposes, such as irrigation, flood control, river diversion, soil-retention, or a combination of these functions. The impermeability of Roman dams was increased by the introduction of waterproof hydraulic mortar and especially opus caementicium in the Concrete Revolution. These materials also allowed for bigger structures to be built, like the Lake Homs Dam, possibly the largest water barrier to date, and the sturdy Harbaqa Dam, both of which consist of a concrete core.
Roman builders were the first to realize the stabilizing effect of arches and buttresses, which they integrated into their dam designs. Previously unknown dam types introduced by the Romans include arch-gravity dams, arch dams,;  buttress dams, and multiple-arch buttress dams.
In architecture, a monolith is a structure which has been excavated as a unit from a surrounding matrix or outcropping of rock. Monoliths are found in all types of Roman buildings. They were either: quarried without being moved; or quarried and moved; or quarried, moved and lifted clear off the ground into their position (e.g. architraves); or quarried, moved and erected in an upright position (e.g. columns).
Transporting was done by land or water (or a combination of both), in the later case often by special-built ships such as obelisk carriers. For lifting operations, ancient cranes were employed since ca. 515 BC, such as in the construction of Trajan's Column.
An obelisk is a tall, four-sided, narrow tapering monument which ends in a pyramid-like shape at the top. These were originally called "tekhenu" by the builders, the Ancient Egyptians. The Greeks who saw them used the Greek 'obeliskos' to describe them, and this word passed into Latin and then English. The Romans commissioned obelisks in an ancient Egyptian style. Examples include:
Roman gardens were influenced by Egyptian, Persian, and Greek gardening techniques. In Ancient Latium, a garden was part of every farm. According to Cato the Elder, every garden should be close to the house and should have flower beds and ornamental trees. Horace wrote that during his time flower gardens became a national indulgence.
Gardens were not reserved for the extremely wealthy. Excavations in Pompeii show that gardens attaching to residences were scaled down to meet the space constraints of the home of the average Roman. Modified versions of Roman garden designs were adopted in Roman settlements in Africa, Gaul, and Britannia. As town houses were replaced by tall insula (apartment buildings), these urban gardens were replaced by window boxes or roof gardens.
A triumphal arch is a monumental structure in the shape of an archway with one or more arched passageways, often designed to span a road. The origins of the Roman triumphal arch are unclear. There were precursors to the triumphal arch within the Roman world; in Italy, the Etruscans used elaborately decorated single bay arches as gates or portals to their cities. Surviving examples of Etruscan arches can still be seen at Perugia and Volterra. The two key elements of the triumphal arch – a round-topped arch and a square entablature – had long been in use as separate architectural elements in ancient Greece. The innovation of the Romans was to these elements in a single free-standing structure. The columns became purely decorative elements on the outer face of arch, while the entablature, liberated from its role as a building support, became the frame for the civic and religious messages that the arch builders wished to convey. Little is known about how the Romans viewed triumphal arches. Pliny the Elder, writing in the first century AD, was the only ancient author to discuss them. He wrote that they were intended to "elevate above the ordinary world" an image of an honoured person usually depicted in the form of a statue with a quadriga.
The first recorded Roman triumphal arches were set up in the time of the Roman Republic. Generals who were granted a triumph were termed triumphators and would erect fornices or honorific arches bearing statues to commemorate their victories. Roman triumphal practices changed significantly at the start of the imperial period when the first Roman Emperor Augustus decreed that only emperors would be granted triumphs. The triumphal arch changed from being a personal monument to being an essentially propagandistic one, serving to announce and promote the presence of the ruler and the laws of the state. Arches were not necessarily built as entrances, but – unlike many modern triumphal arches – they were often erected across roads and were intended to be passed through, not round. Most Roman triumphal arches were built during the imperial period. By the fourth century AD there were 36 such arches in Rome, of which three have survived – the Arch of Titus (AD 81), the Arch of Septimius Severus (203-205) and the Arch of Constantine (312). Numerous arches were built elsewhere in the Roman Empire. The single arch was the most common, but many triple arches were also built, of which the Triumphal Arch of Orange (circa AD 21) is the earliest surviving example. From the 2nd century AD, many examples of the arcus quadrifrons – a square triumphal arch erected over a crossroads, with arched openings on all four sides – were built, especially in North Africa. Arch-building in Rome and Italy diminished after the time of Trajan (AD 98-117) but remained widespread in the provinces during the 2nd and 3rd centuries AD; they were often erected to commemorate imperial visits.
The ornamentation of an arch was intended to serve as a constant visual reminder of the triumph and triumphator. The façade was ornamented with marble columns, and the piers and attics with decorative cornices. Sculpted panels depicted victories and achievements, the deeds of the triumphator, the captured weapons of the enemy or the triumphal procession itself. The spandrels usually depicted flying Victories, while the attic was often inscribed with a dedicatory inscription naming and praising the triumphator. The piers and internal passageways were also decorated with reliefs and free-standing sculptures. The vault was ornamented with coffers. Some triumphal arches were surmounted by a statue or a currus triumphalis, a group of statues depicting the emperor or general in a quadriga. Inscriptions on Roman triumphal arches were works of art in themselves, with very finely cut, sometimes gilded letters. The form of each letter and the spacing between them was carefully designed for maximum clarity and simplicity, without any decorative flourishes, emphasizing the Roman taste for restraint and order. This conception of what later became the art of typography remains of fundamental importance down to the present day.
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