Древнеримские мосты: Инженерное искусство и технологии строительства

Bridges built by ancient Romans

The ancient Romans were the first civilization to build large, permanent bridges. Early Roman bridges used techniques introduced by Etruscan immigrants, but the Romans improved those skills, developing and enhancing methods such as arches and keystones. There were three major types of Roman bridge: wooden, pontoon, and stone. Early Roman bridges were wooden, but by the 2nd century stone was being used. Stone bridges used the arch as their basic structure, and most used concrete, the first use of this material in bridge building.

Following the conquests of Tarquinius Priscus, Etruscan engineers migrated to Rome, bringing with them their knowledge of bridge building techniques. The oldest bridge in ancient Rome was the Pons Sublicius. It was built in the 6th century BCE by Ancus Marcius over the Tiber River. The Romans improved on Etruscan architectural techniques. They developed the voussoir, stronger keystones, vaults, and superior arched bridges. Roman arched bridges were capable of withstanding more stress by dispersing forces across bridges. By the 2nd century BC, the Romans had further refined their bridge building techniques, using stronger materials such as volcanic ash, lime and gypsum. Also, they began to use iron clamps to hold together bridges, constructing midstream arches, and pentagonal stones to allow for wider vaults. According to Canadian classicist John Peter Oleson, no known stone bridges existed in Italy before the 2nd century BCE. This view is not supported unanimously: Spanish engineer Leonardo Fernández Troyano suggested that stone bridges have existed since Pre Roman Italy. Between 150 and 50 BCE, many stone Roman bridges were built, the Pons Aemilius being the first. Engineers began to use stone instead of wood to exemplify the Pax Romana and to construct longer lasting bridges. These were the first large scale bridges ever constructed. By the 2nd century Roman techniques had declined, and they had been mostly lost by the 4th century. The Ponte Sant'Angelo, built during the reign of Hadrian, has five arches each with a span of .

When building bridges across moving bodies of water, Roman engineers would begin by laying a foundation. At first, they used heavy timbers as deep foundations in the riverbed, but a later technique involved using watertight walls to redirect the water and then laying a stone foundation in the area. To aid in the construction of a foundation, work was exclusively done during the dry season. This ensured as many piers as possible were accessible. There is some evidence that in order to construct bridges rivers were diverted. Such a practice might have been performed by Trajan when constructing his Danube bridge. Roman engineers might have diverted rivers using rudimentary methods and tools. Sometimes dirt was added to the foundation. The foundation of a bridge could either be built above or below water level. Building the bridge above water level resulted in a need for a wider span. Later in Roman history arches started to become semi circular. Sometimes arches were segmented, or not semicircular. giving the bridge an unusually flat profile unsurpassed for more than a millennium. The late Roman Karamagara Bridge in Cappadocia in eastern Turkey may represent the earliest surviving bridge featuring a pointed arch, though it is now submerged by the Keban Dam. Bridges had abutments 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 arches of a bridge, allowing each to be built separately. Piers were usually twenty six feet thick and framed with starlings. The late antique Karamagara Bridge represents an early example of the use of pointed arches. Roman piers were thick enough to support the pressure of an arch. Stone arches allowed bridges to have much longer spans. Some bridges had aprons. They were used to surround piers. Usually, the aprons covered the area of the stream bed near the bridge. Travertine limestone and tuff were used to build Roman bridges, The brick bridges that were built were generally used by the military, and they used construction techniques called opus vittatum and opus mixtum, the latter alternating rows of bricks in opus reticulatum. These bridges were supported by wooden trestles spanned by horizontal timbers and reinforced with struts, and they were possibly cantilevered. In order to simplify the process of cutting trees, multiple shorter timbers were used. Other early techniques used to build wooden bridges involved barges, 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 cofferdams, which are enclosures build to pump water out of an area. The base for the foundation of the bridge would be put in this area. 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. Other early wooden bridges used post and lintel construction.

Pontoon bridges were built by laying boats from side to side across a river.

The costs of building and repairing bridges, known as opus 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). The Alcántara Bridge in Lusitania, for example, was built at the expense of 12 local municipalities, whose names were added on an inscription. Later, in the Roman Empire, the local lords of the land had to pay tithes to the empire for opus pontis. The Anglo Saxons continued this practice with bricg geworc, a literal translation of opus pontis.

Built in 142 BC, the Pons Aemilius, later named Ponte Rotto (broken bridge), is the oldest Roman stone bridge in Rome, with only one surviving arch and pier. However, evidence suggests only the abutment is original to the 2nd century BC while the arch and pier perhaps date to a reconstruction during the reign of Augustus (27 BC – 14 AD). The Pons Fabricius, built in 62 BC during the late Republic, is the oldest Roman bridge that is still intact and in use. The largest Roman bridge was Trajan's Bridge over the lower Danube, constructed by Apollodorus of Damascus, which remained for over a millennium the longest bridge to have been built both in terms of overall and span length.

Roman engineers built stone arch or stone pillar bridges over all major rivers of their Imperium, save two: the Euphrates, which lay at the frontier to the rival Persian empires, and the Nile, 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 Rhine, 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 (the Roman Bridge at Mainz, Caesar's Rhine bridges, the Roman Bridge at Koblenz, the Roman Bridge at Cologne). For rivers with strong currents and to allow swift army movements, pontoon bridges were also routinely employed. Judging by 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.