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Roman bridges, built by ancient Romans, were the first large and lasting bridges built.Roman bridges were built with stone and had the arch as its basic structure. Most utilized concrete as well.Built in 142 BC, the Pons Aemilius, later named Ponte Rotto (broken bridge) is the oldest Roman stone bridge in Rome, Italy.The biggest Roman bridge was Trajan's bridgeover 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. They were most of the time at-least 60 ft above the body of water.The longest Roman stone arch was probably Severan Bridge of 34 m, but there are indications of longer arches. The Roman architect Vitruvius tells us that in order to lay the foundations and supporting pillars the Romans would construct water tight vessels, rather like barrels. These were made of wood bound by metal. In order to provide water resistance the barrels could be lined with pitch or clay. By lowering these into the river it was then possible to divert the water from the place of work in order to dig down to build foundations. The foundations could be lain directly onto hard rock if it was found or onto wooden piles driven deep into the river bed. This last solution is relatively durable as is demonstrated by the result achieved with Venice! The wet mud and the lack of oxygen prevents the action of the bacteria which would in other cases destroy the wood.The Romans also used cement, which reduced the variation of strength found in natural stone. One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered. Once the foundations had been laid the bottom portion of the pillar could be built within the "barrel" and from there brought up to the required height above the water level by means of scaffolding. As already described, the arches would be built by creating a truss to support the work until the arch had been spanned and was capable of supporting itself. The Pons Subiacus, the rope-and-timber suspension bridge over the Tiber, crossing the river at Insula Tiberina, was an important landmark from the earliest days of the republic. But, for the purposes of this review, we shall only consider a small selection of masonry bridges. The single or multi-span arches (really, vaults) of Roman bridges are often built in concrete but faced in blocks of ashlar, or in smaller examples, in irregular blocks or rubble. The study of Roman bridge construction and design is important because some of the earliest and boldest uses of concrete technology was invested in bridges and aqueducts; therefore, they represent pioneering developments influencing vaulted architecture itself. Or, to put it more dramatically, without the ability to master the 32-meter span of distant Ponte d'Augusto (see below), there could have been no Pantheon in Rome. |
