Roman (Edited from Wikipedia)

SUMMARY

Roman bridges, built by ancient Romans, were the first large and lasting bridges built. Roman bridges were built with stone and had the as the basic structure. Most utilized as well, which the Romans were the first to use for bridges.

As with the and the the Romans were the first to fully realize the potential of for construction.

A compiled by the engineer Colin O'Connor features 330 Roman stone bridges for traffic, 34 Roman timber bridges and 54 Roman bridges, a substantial part still standing and even used to carry vehicles. A more complete survey by the Italian scholar Vittorio Galliazzo found 931 Roman bridges, mostly of stone, in as many as 26 different countries (including former Yugoslavia).

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 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 and Aqueduct. Their bridges featured from an early time onwards flood openings in the piers, e.g. in the Pons Fabricius in (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 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 Bridge in southwestern 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 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

1 individual span length, while the longest extant is the 790 m long Puente Romano at Mérida.

The late Roman Karamagara Bridge in may represent the earliest surviving bridge featuring a pointed arch.

Early Roman arch bridges, influenced by the ancient notion of the ideal form of the circle, often describe a full circle, with the stone arch continuing underground. A typical example is the Pons Fabricius in Rome. Later, Roman masonry bridges rested mostly on semi-circular arches, or, to a lesser extent, on segmental arches. For the later design, which shows an early, local concentration in north-eastern , but can be found scattered throughout the whole empire, the Limyra Bridge, the Alconétar Bridge and the are prime examples. In addition, a number of other arch forms make rare appearances, in some cases of which later deformations cannot be ruled out. The late antique Karamagara Bridge represents an early example for the use of pointed arches.

Roman engineers built stone arch or stone pillar bridges over all major rivers of their , save two: the Euphrates which lay at the frontier to the rival Iranian empires, and the , the longest river in the world, which was 'bridged' as late as 1902 by the British Old Aswan Dam.

The largest rivers to be spanned by solid bridges by the Romans were the Danube and the , the two largest European rivers west of the Eurasian Steppe. The lower Danube was crossed by least two (Trajan's Bridge, Constantine's Bridge) and the middle and lower Rhine by four different bridges (Roman Bridge at , 's Rhine bridges, Roman Bridge at , Roman Bridge at Cologne). For rivers with strong currents and to allow swift army movements, pontoon bridges were also routinely employed. Going from the distinct lack of records of pre-modern solid bridges spanning larger rivers, the Roman feat appears to be unsurpassed anywhere in the world until into the 19th century.

VOUSSOIRS

A voussoir is a wedge-shaped element, typically a stone, used in building an arch or vault.

Although each unit in an arch or vault is a voussoir, two units are of distinct functional importance: the keystone and the springer. The keystone is the center stone or masonry unit at the apex of an arch. The springer is the lowest voussoir on each side, located

2 where the curve of the arch springs from the vertical support or abutment of the wall or pier.

The keystone is often decorated or enlarged. An enlarged and sometimes slightly dropped keystone is often found in Mannerist arches of the 16th century, beginning with the works of Giulio Romano, who also began the fashion for using voussoirs above rectangular openings, rather than a lintel (Palazzo Stati Maccarani, Rome, c. 1522).

The word is a mason's term borrowed in Middle English from French verbs connoting a "turn" (OED). Each wedge-shaped voussoir turns aside the thrust of the mass above, transferring it from stone to stone to the springer's bottom face ('impost'), which is horizontal and passes the thrust on to the supports. Voussoir arches distribute weight efficiently and take maximum advantage of the compressive strength of stone, as in an arch bridge.

In Visigothic and Islamic architecture, the voussoirs are often in alternating colors, usually red and white. This is sometimes found in Romanesque architecture also.

During the 18th and 19th centuries, British bricklayers became aware that, by thickening the vertical mortar joint between regularly shaped bricks from bottom to top, they could construct an elliptical arch of useful strength[citation needed] over either a standard 'former' or over specially constructed timber falsework (temporary structure to be removed once the construction is complete). The bricks used in such an arch are often referred to as 'voussoirs'.

Keystones

A keystone is the wedge-shaped stone piece at the apex of a masonry arch, the generally round one at the apex of a vault. In both cases it is the final piece placed during construction and locks all the stones into position, allowing the arch or vault to bear weight. In both arches and vaults, keystones are often enlarged beyond the structural requirements, and often decorated in some way. Keystones are often placed in the centre of the flat top of openings such as doors and windows, essentially for decorative effect.

Although a masonry arch or vault cannot be self-supporting until the keystone is placed, the keystone experiences the least stress of any of the voussoirs, due to its position at the apex. Old keystones can decay due to vibration, a condition known as bald arch.

3 In a rib-vaulted ceiling, keystones may mark the intersections of two or more arched ribs. For aesthetic purposes, the keystone is sometimes larger than the other voussoirs, or embellished with a boss. Mannerist architects of the 16th century often designed arches with enlarged and slightly dropped keystones, as in the "church house" entrance portal at Colditz Castle. Numerous examples are found in the work of Sebastiano Serlio, a 16th-century Italian Mannerist architect.

ARCH BRIDGE

An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct (a long bridge) may be made from a series of arches, although other more economical structures are typically used today.

In medieval Europe, bridge builders improved on the Roman structures by using narrower piers, thinner arch barrels and lower span-rise ratios on bridges. Gothic pointed arches were also introduced, reducing lateral thrust, and spans increased as with the eccentric Puente del Diablo (1282).

The 14th century in particular saw bridge building reaching new heights. Span lengthes of 40 m, previously unheard of in the history of masonry arch construction, were now reached in places as diverse as (Puente de San Martín), Italy (Castelvecchio Bridge) and (Devil's bridge and Pont Grand) and with arch types as different as semi-circular, pointed and segmental arches. The bridge at Trezzo sull'Adda, destroyed in the 15th century, even featured a span length of 72 m, not matched until 1796.

Constructions such as the acclaimed Florentine segmental arch bridge Ponte Vecchio (1345) combined sound engineering (span-to-rise ratio of over 5.3 to 1) with aesthetical appeal. The three elegant arches of the Renaissance Ponte Santa Trinita (1569) constitute the oldest elliptic arch bridge worldwide. Such low rising structures required massive abutments, which at the Venetian Rialto bridge and the Fleischbrücke in Nuremberg (span-to-rise ratio 6.4:1) were founded on thousands of wooden piles, partly rammed obliquely into the grounds to counteract more effectively the lateral thrust.

In China, the oldest existing arch bridge is the Zhaozhou Bridge of 605 AD, which combined a very low span-to-rise ratio of 5.2:1, with the use of spandrel arches (buttressed with iron brackets). The Zhaozhou Bridge, with a length of 167 feet (51 m) and span of 123 feet (37 m), is the world's first wholly stone open-spandrel segmental arch bridge, allowing a greater passage for flood waters. Bridges with perforated

4 spandrels can be found worldwide, such as in China (, 7th century). (Bridge of Arta, 17th century) and (Cenarth Bridge, 18th century).

In more modern times, stone and brick arches continued to be built by many civil engineers, including Thomas Telford, Isambard Kingdom Brunel and John Rennie. A key pioneer was Jean-Rodolphe Perronet, who used much narrower piers, revised calculation methods and exceptionally low span-to-rise ratios. Different materials, such as cast iron, steel and concrete have been increasingly used in the construction of arch bridges.

Construction Materials and Sequence

Stone, brick and other such materials are strong in compression and somewhat so in shear, but cannot resist much force in tension. As a result, masonry arch bridges are designed to be constantly under compression, so far as is possible. Each arch is constructed over a temporary falsework frame, known as a centering. In the first compression arch bridges, a keystone in the middle of the bridge bore the weight of the rest of the bridge. The more weight that was put onto the bridge, the stronger its structure became. Masonry arch bridges use a quantity of fill material (typically compacted rubble) above the arch in order to increase this dead-weight on the bridge and prevent tension from occurring in the arch ring as loads move across the bridge. Other materials that were used to build this type of bridge were brick and unreinforced concrete. When masonry (cut stone) is used the angles of the faces are cut to minimize shear forces. Where random masonry (uncut and unprepared stones) is used they are mortared together and the mortar is allowed to set before the falsework is removed.

Traditional masonry arches are generally durable, and somewhat resistant to settlement or undermining. However, relative to modern alternatives, such bridges are very heavy, requiring extensive foundations. They are also expensive to build wherever labor costs are high.

Where the arches are founded in a watercourse bed (on piers or banks) the water is diverted so the gravel can first be excavated and replaced with a good footing (of strong material). From these, the foundation piers are erected/raised to the height of the intended base of the arches, a point known as the springing.

Falsework centering is fabricated, typically from timbers and boards. Since each arch of a multi-arch bridge will impose a thrust upon its neighbors, it is necessary either that all arches of the bridge be raised at the same time, or that very wide piers be used. The thrust from the end arches is taken into the earth by substantial (vertical) footings at

5 the canyon walls, or by large inclined planes forming in a sense ramps to the bridge, which may also be formed of arches.

The several arches are (or single arch is) constructed over the centering. Once each basic arch barrel is constructed, the arches are (or arch is) stabilized with infill masonry above, which may be laid in horizontal running bond courses (layers). These may form two outer walls, known as the spandrels, which are then infilled with appropriate loose material and rubble.

The road is paved and parapet walls protectively confine traffic to the bridge.

In some locations it is necessary to span a wide gap at a relatively high elevation, such as when a canal or water supply must span a valley. Rather than building extremely large arches, or very tall supporting (difficult using stone), a series of arched structures are built one atop another, with wider structures at the base. Roman civil engineers developed the design and constructed highly refined structures using only simple materials, equipment, and mathematics. This type is still used in canal viaducts and roadways as it has a pleasing shape, particularly when spanning water, as the reflections of the arches form a visual impression of circles or ellipses.

THE ARCH

An arch is a curved structure that spans a space and may or may not support weight above it. Arch may be synonymous with vault, but a vault may be distinguished as a continuous arch forming a roof. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture, and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.

An arch is a pure compression form. It can span a large area by resolving forces into compressive stresses and, in turn eliminating tensile stresses. This is sometimes referred to as arch action. As the forces in the arch are carried to the ground, the arch will push outward at the base, called thrust. As the rise, or height of the arch decreases, the outward thrust increases. In order to maintain arch action and prevent the arch from collapsing, the thrust needs to be restrained, either with internal ties or external bracing, such as abutments.

THE COFFERDAM

A cofferdam (also called a coffer) is a temporary enclosure built within, or in pairs across, a body of water and constructed to allow the enclosed area to be pumped out, creating a dry work environment for the major work to proceed. Enclosed coffers are

6 commonly used for construction and repair of oil platforms, bridge piers and other support structures built within or over water. These cofferdams are usually welded steel structures, with components consisting of sheet piles, wales, and cross braces. Such structures are typically dismantled after the ultimate work is completed.

CIRCULAR PERFECTION

The ancient Greeks viewed perfection as a requisite for beauty and high art. The Pythagoreans held that perfection was to be found in the right proportions and in a harmonious arrangement of parts. The idea that beauty and art were characterized by perfection, was subsequently embraced by Plato, who believed that art ought to be "apt, suitable, without deviations" — in short, "perfect."

From a conviction that perfection was a single quality, the Pythagoreans, Plato and their adherents held that beauty also was a single quality; hence, for every kind of art, there was but one perfect and proper form. stated (De Musica) that, during the early Greek age, musical harmonies that were recognized as perfect were legally binding at public performances.

Similarly, in temple architecture from the 5th century BCE, there were established orders. There were established proportions for Doric temples, and for Ionic temples. Likewise in sculpture, for centuries, it was a matter of dogma that certain proportions of the human body were perfect and obligatory.

There was also a prevalent belief that certain shapes and proportions were in themselves perfect. Plato felt that the perfect proportion was the ratio of the side to the diagonal of a square. His authority was so great that architects and other artists continued using this proportion, even when ignorant of its source, as late as the .

Another early idea — one that was to be espoused by many illustrious writers and artists of various periods — found perfection in the circle and the sphere . Aristotle wrote in the Physica that the circle was "the perfect, first, most beautiful form." wrote in De natura deorum (On the Nature of the Gods): "Two forms are the most distinctive: of solids, the sphere... and of plane figures, the circle... There is nothing more commensurate than these forms."

In a commentary to Aristotle's De coelo et mundo (On the Heavens and Earth), the medieval Pole, Jan of Słupcza, wrote: "The most perfect body ought to have the most perfect form, and such [a body] is heaven, while the most perfect form is the round form, for nothing can be added to it." In a famous illustrated book of prayers from the 15 th century, paradise is depicted as contained within an ideal sphere.

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The Renaissance architect Sebastiano Serlio (1475–1554) stated: "the round form is the most perfect of all.”

The most excellent of 16th-century architects, Andrea Palladio, held that "the most perfect and most excellent" form was "the round form, since of all forms it is the simplest, the most uniform, the strongest, the most capacious" and "is the most suitable for rendering the unity, infinity, uniformity and righteousness of God." This was the same thought as in Jan of Słupcza and in Serlio, and it was one of uncommon durability.

Circular Divinity

The Greek philosopher Anaximander described the world as "endless" (apeiron), Xenophanes — as "the greatest" (megistos). But while they ascribed great qualities to the world, they did not regard it as perfect.

Only Parmenides seems to have considered existence to be "tetelesmenon" ("finished"); and Melissos, his successor in the Eleatic school, said that existence "was entirely" ("pan esti"). Thus both saw perfection in existence; true existence was one, constant, immutable. Moreover, Parmenides thought the world to be finite, limited in all directions, and like a sphere — which was a mark of its perfection.

Parmenides' view was embraced to some extent by Plato. He thought that the world was the work of a good Demiurge, and that this was why order and harmony prevailed in the world. The world was the best, the most beautiful, perfect. It had a perfect shape (spherical) and a perfect motion (circular).

But Plato said nothing about the Demiurge architect-of-the-world himself being perfect. And understandably so, for perfection implied finitude, limits; whereas it was the world, not its creator, that had limits. A similar view was held by Aristotle: the world could be perfect, but God could not.

Only the pantheist Stoics held the divinity to be perfect — precisely because they identified it with the world. Pantheism is the belief that all of reality is identical with divinity, or that everything composes an all-encompassing, immanent god. Pantheists thus do not believe in a distinct personal or anthropomorphic god. Cicero wrote in De natura deorum (On the Nature of the Gods ) that the world "encompasses... within itself all beings... And what could be more nonsensical than denying perfection to an all- embracing being... Besides the world, there is no thing that does not lack something and that is harmonious, perfect and finished in every respect..."

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