John Wolfe-Barry and Horace Jones, Tower Bridge, London, 1886-94

Movable bridges appeared at the end of the 19th century. Barry and Jones built Tower Bridge in London to resolve the problem of commercial traffic. The central structure is a movable roadway that can he raised or lowered to permit the passage of ships along the Thames.

Sir Benjamin Baker, Firth of Forth Bridge, Edinburgh, 1882-89

The bridge is composed of three giant units supported by pylons over a total length of about 2,500 meters; it was perfectly suited to the many visionary works of the period and was immediately popular Very few people criticized the bridge’s appearance, but among them was William Morris, one of the fathers of modernism, who called it ‘the supremest specimen of all ugliness?.

The Coalbrookdale Bridge over the Severn River in England – built in 1779 to a design by Abraham Darby and John Wilkinson and made entirely in cast iron – can be taken as the first member of a vastly numerous family, which beginning at the end of the 18th century revolutionized landscapes and methods of transportation while also revealing the level of complexity already reached by engineering. In 1801 James Finlay patented a system of trusses to stiffen the decks of suspension bridges, a construction method of fundamental importance that was further developed with the introduction of cables and iron links. During the first half of the century, numerous bridges were built in England using this technique, from the Union Bridge at Tweed to the Clifton Bridge near Bristol.

The suspension bridge system was perfected by Josiah White and Erskine Hazard in crossing the Schuylkill River in Pennsylvania (1816) and by the Seguin brothers at Tournon-Tain over the Rhone (1825); both bridges were early uses of bundled wire in place of wrought-iron chains. Johann August Roebling – author of railroad bridges at Niagara Falls (1855) and over the Ohio at Cincinnati (1867) – brought about a significant technical improvement in suspension bridges thanks to the use of wire cables and stiffening trusses, which were more structurally solid than preceding versions. At the same time steel tended to replace iron, and designers concentrated on obtaining lighter structures using smaller quantities of material but guaranteeing greater tensile strength and elasticity. Gustave Eiffel was also a leader in bridge building. His bridge over the Douro River (1878) is composed of five piers and a central parabolic arch that supports a continuous girder, and his railway bridge over the Truyere at Garabit (1884), the quintessence of economy and elegance, uses tapering iron towers.