Theancient Romans were the first civilization to build large, permanentbridges.[1] Early Roman bridges used techniques introduced byEtruscanimmigrants, but the Romans improved those skills, developing and enhancing methods such asarches andkeystones. There were three major types ofRoman bridge: wooden, pontoon, and stone. Early Roman bridges were wooden, but by the 2nd century BC stone was being used. Stone bridges used the arch as theirbasic structure, and most usedconcrete, the first use of this material in bridge-building.
Following the conquests ofTarquinius Priscus,Etruscan engineers migrated to Rome, bringing with them their knowledge of bridge-building techniques. The oldest bridge inancient Rome was thePons Sublicius.[2][3] It was built in the 6th century BC byAncus Marcius over theTiber River.[3][4] The Romans improved onEtruscan architectural techniques. They developed thevoussoir, strongerkeystones,vaults, and superior arched bridges.[5][6] Roman arched bridges were capable of withstanding more stress by dispersing forces across bridges.[7] Many Roman bridges had semicircular arches, but a few weresegmental, i.e. with an arc of less than 180 degrees.[8]
By the 2nd century BC, the Romans had further refined their bridge-building techniques, using stronger materials such asvolcanic ash,lime andgypsum. Also, they began to useiron clamps to hold together bridges, constructing midstream arches, andpentagonal stones to allow for widervaults.[9] According to Canadian classicistJohn Peter Oleson, no known stone bridges existed in Italy before the 2nd century BC.[7][10] This view is not supported unanimously: Spanish engineerLeonardo Fernández Troyano suggested that stone bridges have existed sincePre-Roman Italy.[11][12]
Between 150 and 50 BC, many stone Roman bridges were built, thePons Aemilius being the first.[2][13] Engineers began to use stone instead of wood to exemplify thePax Romana and to construct longer-lasting bridges.[14] These were the first large-scale bridges ever constructed.[9] Bridges were constructed by the Roman government to serve the needs of themilitary and the empire's administration. Sometimes roads and bridges were used for commercial purposes, but this was rare as boats better served the needs of theRoman economy.[15]
By the 2nd century Roman techniques had declined, and they had been mostly lost by the 4th century.[3] Some Roman bridges are still used today, such as thePons Fabricius, and even after theFall of the Western Roman Empire, engineers copied their bridges.[16] Roman bridge-building techniques persisted until the 18th century:[3] for example, the prevalence of arches in bridges can be attributed to the Romans.[15]
Roman bridges were much larger than the bridges of other civilizations. They could be anywhere from 4.6 to 18.3 metres (15 to 60 ft) long. By the time ofAugustus around the turn of the 1st millennium the maximum span of Roman bridges increased from around 24 metres (79 ft) in 142 BC to 35 metres (115 ft).[17] ThePonte Sant'Angelo, built during the reign ofHadrian, has five arches each with a span of 18 metres (59 ft).[11] Abridge inAlcántara has piers 1 metre (3 ft 3 in) wide, 47 metres (154 ft) high, and arches with a span of 1.3 metres (4 ft 3 in). Another bridge over the Bibey River inGalicia has a pier 1 metre (3 ft 3 in) wide, arches with a 4.3-metre (14 ft) span, 6-and-9-metre (20 and 30 ft) side arches, and an arch spanning 18.5 metres (61 ft). Wider spans increase the bridge's drainage, reduce water pressure on thespandrels, and reduced the bridge's weight.[11]Trajan's Bridge over theDanube featured open-spandrel segmental arches made of wood (standing on 40 metres (130 ft) high concrete piers). This was to be the longest arch bridge for a thousand years both in terms of overall and individual span length. The longest extant Roman bridge is the 790-metre (2,590 ft)Puente Romano atMérida.[18]
Roman engineers would begin by laying a foundation for building bridges across moving bodies of water. At first, they used heavy timbers aspilings in the riverbed, but a later technique involved usingwatertight walls to redirect the water and then laying a stone foundation in the area. Work was exclusively done during thedry season to aid in constructing a foundation. This ensured as many piers as possible were accessible. There is some evidence that to construct bridges rivers were diverted. Trajan might have performed such a practice when constructing his Danube bridge. Roman engineers might have diverted rivers using rudimentary methods and tools. Sometimes dirt was added to the foundation. A bridge's foundation could be built above or belowwater level. Building the bridge above water level resulted in a need for a wider span.[16][15] Bridge's tunnels and spandrels were designed to decrease the weight of the bridge and function asflood arches.[15]
ThePons Aemilius probably had stone piers with wooden roadbeds and arches.[2] They were rebuilt in stone in 142 BC and either extended from the abutments to thepiers or vice versa. Throughout Roman history, brick or stone arches supported bridges' weight.[16] Roman engineers built bridges with one long arch instead of several smaller ones. This practice made construction easier, as they only needed to build one arch on land, instead of many in water. Roman arches were semi-circular and usedvoussoirs with equal dimensions andconic sections with equal circumference.[11][19] Later in Roman history arches started to becomesemi-circular.[20][21] Sometimes arches weresegmented, or not semicircular.[8] The Romans invented this technique. Segmented arches allowed greater amounts of flood water to pass, preventing the bridge from being swept away and allowing it to be lighter. TheBridge near Limyra in southwesternTurkey has 26 segmental arches with an average span-to-rise ratio of 5.3:1,[22] giving the bridge an unusually flat profile unsurpassed for more than a millennium.[23] The late RomanKaramagara Bridge inCappadocia in eastern Turkey may represent the earliest surviving bridge featuring a pointed arch. However, it is now submerged by theKeban Dam.[18] Roman arches were unable to fit into the arch springings properly, forcing the base of the arches upwards.
In the2nd century, arches became thinner, and spandrels became flat and pierced with holes. They were constructed using a wooden frame to hold wedge-shaped blocks in place. Afterwards, the wooden frame was removed, but the weight of thekeystone, the last block to be put in place, held it together.[24] Bridges hadabutments at each end and piers in the middle, these two design features carrying most of the bridge's weight. Abutments could be constructed in the manyarches of a bridge, allowing each to be built separately.[16] Piers were usually twenty-six feet thick andframed withstarlings. The Karamagara Bridge represents an early example of the use ofpointed arches.
Romanpiers were thick enough to support the pressure of an arch. Stone arches allowed bridges to have much longer spans.[9] Usually, iron clamps covered inlead were used to build piers. Because of poor performance underwater, Roman piers were often destroyed over time.[15] Bridges that survived to the modern day were often furnished withcut waters on the upstream side and a flat downstream face, though some bridges, such as a bridge inChester, are exceptions.[15]
Twoniches carryingcornices were inserted betweenpilasters. They were then put above the framed starlings. Roman bridges hadspandrels, between which images ofdolphins were often inserted.[3] They rarely had wide spans and thick piers withbow-shaped piers that used small openings to allow for the flow of water. During construction, cranes were used to move materials and lift heavy objects.[25] Some bridges hadaprons. They were used to surround piers. Usually, the aprons covered the area of thestream bed near the bridge.[15]
Marcus Vipsanius Agrippa usedashlar and bricks to cover the outside of bridges and concrete forfootings and water channels. Ashlar was used because large amounts of wood were needed tocast the concrete.[26]Travertine limestone andtuff were used to build Roman bridges,[7] or they could be made of dry rubble or concrete. Often the building materials varied insmoothness, orrustication. Other bridges were made ofbossed limestone combined with cornices, voussoirs and slabs. Sometimesbedrock,buttresses, andvaults were used to construct bridges.[7] Bridges built in Iberia tended to have cylindrical vault geometry.[25] In the first half of the 2nd century BC, blocks of stone held together with ironclamps were used to aid in the construction of bridges.
AlthoughRoman bricks were used to build many bridges, they were far more commonly used to build aqueducts. Bridges built from bricks were rare as bricks often failed to surviveerosion.[27] The brick bridges that were built were generally used by themilitary, and they used construction techniques calledopus vittatum andopus mixtum, the latter alternating rows of bricks inopus reticulatum.[14] Examples are bridges inCarmona,Palomas,Extremadura, and thePonte della Chianche in Italy. One brick bridge inTicino,Switzerland, has stone arches and brick spandrels.[11] Bricks were sometimes used to create parts of bridges, such asvaults, piers withwelding joints, and brick andmortarrubble.[8]
Early Roman bridges were wooden, including one constructed byApollodorus and the Pons Sublicius, the oldest bridge in ancient Rome, and they were probably common across northern Europe and theTyrrhenian coast;[15] however, because of their lack of durability few have survived to the modern day.[28] These bridges were supported by woodentrestles spanned by horizontal timbers and reinforced withstruts, and they were possiblycantilevered. In order to simplify the process of cutting trees, multiple shorter timbers were used.[3] Wooden poles were driven into the ground, and flat pieces of timber laid across them to create a flat surface.[29]
Other early techniques used to build wooden bridges involvedbarges, sometimes they weremoored side by side. Workmen would raise weights, sometimes by rope, then it would fall down onto the piles. This method of construction, calledpile driving, was necessary for wooden bridges to properly function. Because this technique createdcofferdams, which are enclosures build to pump water out of an area.[30] The base for the foundation of the bridge would be put in this area.[15] Cofferdams were constructed of many piles held together. It is possible the piles were interconnected, likely to improve positioning,waterproofness, or both. Cofferdams would have been sealed with packed clay.[15] The cofferdams also needed to be consistently dry. In order to achieve this, engineers would use tools such as buckets to drain the water.[15] Wooden bridges could be burned to stop an attacker, or dismantled quickly.[7][31] For example, according toLivy, during a battle against theSabines the Romans set one of their wooden bridges on fire, driving the enemy back.[32] Other early wooden bridges usedpost and lintel construction.
Pontoon bridges were built by laying boats from side to side across a river.[29][5] DuringJulius Caesar'scampaign inGermany, he builtbridges by driving wooden piles into thestream bed from floating platforms and fixing beams atright angles across them to create trestles.Trajan built another bridge supported by stone during theDacian Wars.[4] Roman engineers gradually developed new techniques to build bridges, such as oval-shaped bases and pierced bases to facilitate the movement of water. Many bridges would havemarblereliefs orcarvings, but these bridges were likely used exclusively bygovernment officials because of the difficulty and expense of carving marble artwork.
There were three major types of Roman bridges. These were wooden, pontoon, and stone bridges. A list of Roman bridges compiled by the engineer Colin O'Connor features 330stone bridges for traffic, 34timber bridges and 54aqueduct bridges, a substantial number still standing and even used to carry vehicles.[23] 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 formerYugoslavia; see right table).[19] A segmental arch is an arch that is less than a semicircle.[8] The Romans built both single spans and lengthy multiple-archaqueducts, such as thePont du Gard andSegovia Aqueduct. Their bridges often had flood openings in the piers, e.g. in thePons Fabricius in Rome (62 BC), one of the world's oldest major bridges still standing.
There were two main types of wooden bridge in Britain. Small timber bridges withgirders, and large ones made of stone and wood. Throughout the rest of the Roman world, except for northern Europe, arched bridges made of stone were common. This was likely due to the climate and rivers of the regions. Rivers were much calmer and water levels were lower in the southern parts of the Empire. This ensured foundations were easy to construct. While in the northern parts it was much harder to lay down foundations due to the high water level, muddy water, and substantial waterflow.[33]
| Europe | 830 | Asia | 74 | Africa | 57 |
|---|---|---|---|---|---|
| Italy | 460 | Turkey | 55 | Tunisia | 33 |
| Spain | 142 | Syria | 7 | Algeria | 18 |
| France | 72 | Jordan | 5 | Libya | 5 |
| Germany | 30 | Lebanon | 4 | ||
| United Kingdom | 29 | Israel | 2 | ||
| Portugal | 14 | Iran | 1 | ||
| Yugoslavia | 13 | ||||
| Switzerland | 11 | ||||
| Greece | 10 | ||||
| Netherlands | 4 | ||||
| Bulgaria | 3 | ||||
| Luxemburg | 3 | ||||
| Albania | 2 | ||||
| Austria | 2 | ||||
| Belgium | 2 | ||||
| Romania | 2 | ||||
| Hungary | 1 |
The costs of building and repairing bridges, known asopus pontis ("bridge work"), were the responsibility of multiple local municipalities. Their shared costs prove Roman bridges belonged to the region overall, and not to any one town (or two, if on a border). TheAlcántara Bridge inLusitania, for example, was built at the expense of 12 local municipalities, whose names were added on an inscription.[35] Later, in theRoman Empire, the local lords of the land had to pay tithes to the empire foropus pontis.[36][37] TheAnglo-Saxons continued this practice withbricg-geworc, a literal translation ofopus pontis.[38]
Built in 142 BC, thePons Aemilius, later named Ponte Rotto (broken bridge), is the oldest Roman stone bridge inRome, with only one surviving arch and pier. However, evidence suggests only theabutment is original to the 2nd century BC while the arch and pier perhaps date to a reconstruction during the reign ofAugustus (27 BC – 14 AD).[39] The Pons Fabricius, built in 62 BC during the late Republic, is the oldest Roman bridge that is still intact and in use.[40] The largest Roman bridge wasTrajan's Bridge over the lowerDanube, constructed byApollodorus of Damascus, which remained for over a millennium the longest bridge to have been built both in terms of overall and span length.[41]
Roman engineers built stone arch or stone pillar bridges over all major rivers of the Empire save two: theEuphrates, which lay at the frontier in theRoman–Persian Wars, and theNile, the longest river in the world, which was bridged as late as 1902 by the BritishOld Aswan Dam.[42] The largest rivers to be spanned by solid bridges by the Romans were theDanube and theRhine,the two largest European rivers west of theEurasian 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 (theRoman Bridge at Mainz,Caesar's Rhine bridges, theRoman Bridge at Koblenz, theRoman Bridge at Cologne). For rivers with strong currents and to allow swift army movements,pontoon bridges were also routinely employed.[43] Judging by the distinct lack of records of pre-modern solid bridges spanning larger rivers,[11] the Roman feat appears to be unsurpassed anywhere in the world until into the 19th century.
The Romans were the first builders in Europe, perhaps the first in the world, fully to appreciate the advantages of the arch, the vault and the dome.
The ends of the bridge called abutments, were built on each side, and piers were situated in the middle. The abutments and piers carried most of the bridge's weight.
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