Editing Roman bridge (section)

=== 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.