Editing Roman bridge (section)

== Construction ==
=== Measurements ===
[[File:Sant Angelo bridge.jpg|thumb|left|[[Ponte Sant'Angelo]]]]
Roman bridges were much larger than the bridges of other civilizations. They could be anywhere from {{convert|4.6|to|18.3|m}} long. By the time of [[Augustus]] around the turn of the 1st millennium the maximum span of Roman bridges increased from around {{convert|24|m}} in 142 BC to {{convert|35|m}}.<ref>{{Cite book |last1=Gagarin |first1=Michael |url=https://books.google.com/books?id=lNV6-HsUppsC&q=Bridges+in+Ancient+Rome |title=The Oxford Encyclopedia of Ancient Greece and Rome |last2=Fantham |first2=Elaine |author2-link=Elaine Fantham |date=2010 |publisher=Oxford University Press |isbn=978-0-19-517072-6 |pages=25 |language=en}}</ref> The [[Ponte Sant'Angelo]], built during the reign of [[Hadrian]], has five arches each with a span of {{convert|18|m}}.<ref name="troyano" /> A bridge in [[Alcántara]] has piers {{convert|1|m}} wide, {{convert|47|m}} high, and arches with a span of {{convert|1.3|m}}. Another bridge over the Bibey River in [[Galicia (Spain)|Galicia]] has a pier {{convert|1|m}} wide, arches with a {{convert|4.3|m|adj=on}} span, {{convert|6|and|9|m|adj=on}} side arches, and an arch spanning {{convert|18.5|m}}. Wider spans increase the bridge's drainage, reduce water pressure on the [[spandrels]], and reduced the bridge's weight.<ref name="troyano" /> [[Trajan's Bridge]] over the [[Danube]] featured open-spandrel segmental arches made of wood (standing on {{convert|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. The longest extant Roman bridge is the {{convert|790|m|adj=on}} [[Puente Romano]] at [[Mérida, Spain|Mérida]].<ref name=":132">{{harvnb|Galliazzo|1995|pp=92, 93 (fig. 39)}}</ref>

=== Stone bridges ===
Roman engineers would begin by laying a foundation for building bridges across moving bodies of water. At first, they used heavy timbers as [[pilings]] in the riverbed, but a later technique involved using [[cofferdam|watertight walls]] to redirect the water and then laying a stone foundation in the area. Work was exclusively done during the [[dry 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 below [[water level]]. Building the bridge above water level resulted in a need for a wider span.<ref name="maynard" /><ref name="ruddock" /> Bridge's tunnels and spandrels were designed to decrease the weight of the bridge and function as [[flood arch]]es.<ref name="ruddock" />

[[File:Bender_-_Pons_Aemilius.JPG|thumb|left|[[Pons Aemilius]]]]
The [[Pons Aemilius]] probably had stone piers with wooden roadbeds and arches.<ref name="aldrete" /> They were rebuilt in stone in 142 BC and either extended from the abutments to the [[Pier (architecture)|piers]] or vice versa. Throughout Roman history, brick or stone arches supported bridges' weight.<ref name="maynard" /> 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 used [[voussoir]]s with equal dimensions and [[conic section]]s with equal circumference.<ref name="troyano" /><ref name=":143">{{harvnb|Galliazzo|1994|p=2 (Indice)}}</ref> Later in Roman history arches started to become [[Semicircle|semi-circular]].<ref>{{harvnb|Galliazzo|1995|pp=429–437}}</ref><ref>{{harvnb|O'Connor|1993|p=171}}</ref> Sometimes arches were [[Segmental arch|segmented]], or not semicircular.<ref name="beall" /> 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. The [[Bridge near Limyra]] in southwestern [[Turkey]] has 26 segmental arches with an average span-to-rise ratio of 5.3:1,<ref>{{harvnb|O'Connor|1993|p=126}}</ref> giving the bridge an unusually flat profile unsurpassed for more than a millennium.<ref name=":153">{{harvnb|O'Connor|1993|p=187ff}}</ref> The late Roman [[Karamagara Bridge]] in [[Cappadocia]] in eastern Turkey may represent the earliest surviving bridge featuring a pointed arch. However, it is now submerged by the [[Keban Dam]].<ref name=":132"/> Roman arches were unable to fit into the arch springings properly, forcing the base of the arches upwards. 

In the [[2nd 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 the [[Keystone (architecture)|keystone]], the last block to be put in place, held it together.<ref>{{Cite book |last=Uhl |first=Xina M. |url=https://books.google.com/books?id=oLPXDwAAQBAJ&dq=Construction+of+Roman+bridges&pg=PA34 |title=How STEM Built the Roman Empire |date=2019-12-15 |publisher=The Rosen Publishing Group, Inc |isbn=978-1-7253-4154-8 |pages=33–34 |language=en}}</ref> Bridges had [[abutment]]s 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 many [[arch]]es of a bridge, allowing each to be built separately.<ref name="maynard">{{Cite book |last=Maynard |first=Charles W. |url=https://books.google.com/books?id=Za6fFqskPFUC&dq=Bridges+in+Ancient+Rome&pg=PA15 |title=The Technology of Ancient Rome |date=15 January 2006 |publisher=The Rosen Publishing Group, Inc |isbn=978-1-4042-0556-7 |pages=15–21 |language=en |quote=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.}}</ref> Piers were usually twenty-six feet thick and [[Framing (construction)|framed]] with [[Starling (structure)|starlings]]. The Karamagara Bridge represents an early example of the use of [[pointed arch]]es.

Roman [[Pier (architecture)|piers]] were thick enough to support the pressure of an arch. Stone arches allowed bridges to have much longer spans.<ref name="dupre" /> Usually, iron clamps covered in [[lead]] were used to build piers. Because of poor performance underwater, Roman piers were often destroyed over time.<ref name="ruddock" /> Bridges that survived to the modern day were often furnished with [[starling (structure)|cut waters]] on the upstream side and a flat downstream face, though some bridges, such as a bridge in [[Chester]], are exceptions.<ref name="ruddock" />

Two [[niche construction|niches]] carrying [[cornice]]s were inserted between [[pilaster]]s. They were then put above the framed starlings. Roman bridges had [[spandrel]]s, between which images of [[dolphin]]s were often inserted.<ref name="whitney" /> They rarely had wide spans and thick piers with [[Bow (watercraft)|bow]]-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.<ref name=":72">{{Cite book |last1=Arêde |first1=António |url=https://books.google.com/books?id=K0uzDwAAQBAJ&dq=Construction+of+Roman+bridges&pg=PA104 |title=Proceedings of ARCH 2019: 9th International Conference on Arch Bridges |last2=Costa |first2=Cristina |date=2019-10-01 |publisher=Springer Nature |isbn=978-3-030-29227-0 |pages=31–34 |language=en}}</ref> Some bridges had [[Apron (architecture)|aprons]]. They were used to surround piers. Usually, the aprons covered the area of the [[stream bed]] near the bridge.<ref name="ruddock" />

[[Marcus Vipsanius Agrippa]] used [[ashlar]] and bricks to cover the outside of bridges and concrete for [[foundation (engineering)|footings]] and water channels. Ashlar was used because large amounts of wood were needed to [[casting (metalworking)|cast]] the concrete.<ref>{{Cite book |last=Garrison |first=Ervan G. |url=https://books.google.com/books?id=3XuCDwAAQBAJ&dq=History+of+Roman+bridges&pg=PT113 |title=History of Engineering and Technology: Artful Methods |date=2018-12-19 |publisher=Routledge |isbn=978-1-351-44047-9 |language=en}}</ref> [[Travertine]] limestone and [[tuff]] were used to build Roman bridges,<ref name="oleson" /> or they could be made of dry rubble or concrete. Often the building materials varied in [[smoothness]], or [[Rustication (architecture)|rustication]]. Other bridges were made of [[Boss (architecture)|bossed]] limestone combined with cornices, voussoirs and slabs. Sometimes [[bedrock]], [[buttress]]es, and [[Vault (architecture)|vaults]] were used to construct bridges.<ref name="oleson" /> Bridges built in Iberia tended to have cylindrical vault geometry.<ref name=":72" /> In the first half of the 2nd century BC, blocks of stone held together with iron [[Sleeve coupling|clamps]] were used to aid in the construction of bridges.

=== Brick bridges ===
Although [[Roman brick]]s 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 survive [[erosion]].<ref name=":112">{{Cite book |last1=Yegül |first1=Fikret |url=https://books.google.com/books?id=G8CkDwAAQBAJ&dq=Brick+bridges+Roman&pg=PA153 |title=Roman Architecture and Urbanism: From the Origins to Late Antiquity |last2=Favro |first2=Diane |date=2019-09-05 |publisher=Cambridge University Press |isbn=978-0-521-47071-1 |pages=153 |language=en}}</ref> The brick bridges that were built were generally used by the [[Military of ancient Rome|military]], and they used construction techniques called ''[[opus vittatum]]'' and ''[[opus mixtum]]'', the latter alternating rows of bricks in ''[[opus reticulatum]]''.<ref name="bove" /> Examples are bridges in [[Carmona, Spain|Carmona]], [[Palomas, Badajoz|Palomas]], [[Extremadura]], and the [[Ponte del Chianche|Ponte della Chianche]] in Italy. One brick bridge in [[Ticino]], [[Switzerland]], has stone arches and brick spandrels.<ref name="troyano" /> Bricks were sometimes used to create parts of bridges, such as [[Vault (architecture)|vaults]], piers with [[welding joint]]s, and brick and [[Mortar and pestle|mortar]] [[rubble]].<ref name="beall" />

=== Wooden bridges ===
[[File:Il_ponte_di_Cesare_sul_Reno.jpg|thumb|left|[[Caesar's Rhine bridges|Caesar's Rhine Bridge]]]]
Early Roman bridges were wooden, including one constructed by [[Apollodorus of Damascus|Apollodorus]] and the Pons Sublicius, the oldest bridge in ancient Rome, and they were probably common across northern Europe and the [[Tyrrhenian Sea|Tyrrhenian coast]];<ref name="ruddock" /> however, because of their lack of durability few have survived to the modern day.<ref>{{Cite book |last1=Glick |first1=Thomas F. |url=https://books.google.com/books?id=77y2AgAAQBAJ&dq=Brick+bridges+Roman&pg=PA103 |title=Medieval Science, Technology, and Medicine: An Encyclopedia |last2=Livesey |first2=Steven |last3=Wallis |first3=Faith |date=2014-01-27 |publisher=Routledge |isbn=978-1-135-45932-1 |pages=103 |language=en}}</ref> These bridges were supported by wooden [[Trestle support|trestles]] spanned by horizontal timbers and reinforced with [[strut]]s, and they were possibly [[cantilever]]ed. In order to simplify the process of cutting trees, multiple shorter timbers were used.<ref name="whitney" /> Wooden poles were driven into the ground, and flat pieces of timber laid across them to create a flat surface.<ref name="mcgeough">{{Cite book |last=McGeough |first=Kevin M. |url=https://books.google.com/books?id=tKzvK5YbCJYC&dq=Construction+of+Roman+bridges&pg=PA213 |title=The Romans: An Introduction |date=2009-03-26 |publisher=OUP USA |isbn=978-0-19-537986-0 |pages=213 |language=en}}</ref> 

Other early techniques used to build wooden bridges involved [[barge]]s, sometimes they were [[moored]] side by side. Workmen would raise weights, sometimes by rope, then it would fall down onto the piles. This method of construction, called [[pile driving]], was necessary for wooden bridges to properly function. Because this technique created [[cofferdam]]s, which are enclosures build to pump water out of an area.<ref>Chisholm, Hugh, ed. (1911). "[[wikisource:1911 Encyclopædia Britannica/Cofferdam|Cofferdam]]" . ''[[Encyclopædia Britannica Eleventh Edition|Encyclopædia Britannica]]''. Vol. 6 (11th ed.). Cambridge University Press. p. 649.</ref> The base for the foundation of the bridge would be put in this area.<ref name="ruddock" /> Cofferdams were constructed of many piles held together. It is possible the piles were interconnected, likely to improve positioning, [[Waterproofing|waterproofness]], or both. Cofferdams would have been sealed with packed clay.<ref name="ruddock" /> The cofferdams also needed to be consistently dry. In order to achieve this, engineers would use tools such as buckets to drain the water.<ref name="ruddock" /> Wooden bridges could be burned to stop an attacker, or dismantled quickly.<ref name="oleson" /><ref>{{Cite book |last=Landart |first=Paula |url=https://books.google.com/books?id=S-VxBAAAQBAJ&dq=Bridges+in+Ancient+Rome&pg=PA46 |title=Finding Ancient Rome: Walks in the city |date=5 December 2021 |publisher=Paula Landart |pages=45–46 |language=en}}</ref> For example, according to [[Livy]], during a battle against the [[Sabines]] the Romans set one of their wooden bridges on fire, driving the enemy back.<ref>{{Cite book |last=Livius |first=Titus |url=https://files.romanroadsstatic.com/materials/romans/historians/Livy_Early_History_Rome_1-0.pdf |title=Early History of Rome |pages=43}}</ref> Other early wooden bridges used [[post and lintel]] construction.
[[File:Roman Pontoon Bridge, Column of Marcus Aurelius, Rome, Italy.jpg|thumb|Roman legionaries crossing the Danube River by [[pontoon bridge]], as depicted in a relief on the [[Column of Marcus Aurelius]]]]

=== Pontoon bridges ===

[[Pontoon bridge]]s were built by laying boats from side to side across a river.<ref name="mcgeough" /><ref name="bunson" /> During [[Julius Caesar]]'s [[Gallic Wars|campaign]] in [[Germania|Germany]], he built [[Caesar's Rhine bridges|bridges]] by driving wooden piles into the [[stream bed]] from floating platforms and fixing beams at [[right angle]]s across them to create trestles. [[Trajan]] built another bridge supported by stone during the [[Trajan's Dacian Wars|Dacian Wars]].<ref name="corbishley" /> 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 have [[marble]] [[relief]]s or [[carving]]s, but these bridges were likely used exclusively by [[Roman Constitution|government officials]] because of the difficulty and expense of carving marble artwork.