From Swiss stilt houses to a two-kilometre span, bridges track engineering history
A single railway locomotive can weigh 197 tonnes, which is one reason train lines shy away from graceful curving or cable-hung crossings and stick to stiff straight beams and trusses. The same trade-off between load, span and material has shaped bridge design for six thousand years, since people first drove wooden piles into Swiss lakebeds.
The oldest crossings were logs and boardwalks over creeks and marshes. Pilings, still central to bridge building, held up stilt houses in Switzerland around 4000 BC, and Mycenaean Greeks raised corbel arches such as the Arkadiko Bridge, which survives, in the thirteenth century BC. The Assyrian king Sennacherib carried water toward Nineveh on a stone aqueduct at Jerwan 280 metres long. The Romans then mastered the semicircular arch and cement, some of it made with volcanic ash that set underwater; Trajan's Bridge over the Danube ran more than 900 metres around 105 AD. China's Anji Bridge, completed in 605, is the oldest arch of its open-spandrel segmental type anywhere.
Skills faded in Europe after Rome and returned in the High Middle Ages with works like the Ponte Vecchio. Renaissance writers including Galileo and Palladio brought analytic rigour, and in the late eighteenth century Jean-Rodolphe Perronet and John Rennie flattened the arch, which sped construction, let rivers flow more freely and slimmed the piers.
Metal changed everything. England's cast-iron Iron Bridge of 1781 was the first major crossing built wholly of metal. Railways from the 1820s pushed Brunel, Robert Stephenson and others to build ever larger, and in the Railway Mania years Britain's rail bridges doubled in number, going from 30,000 to 60,000. Cheap steel later in the century allowed lighter trusses and cantilevers and replaced iron bars in suspension cables, while Portland cement made concrete the standard for foundations.
The twentieth century brought record after record, with cable-stayed designs spreading after the Second World War and corrosion-proof polymer composites arriving later. In 2022 the 1915 Çanakkale Bridge in Turkey became the first to span over 2 kilometres.
Source: Bridge
