In ancient times, bridges were built from easily accessed natural resources such as wood, stone, and clay with very limited span lengths, until mortar, the early form of Portland cement, was invented. With mortar material and the arch structure shape, Romans were able to build strong and lightweight bridges and even long viaducts, such as the one shown in Figure 1.1, which is built in the first century. In the seventh century, China was able to employ cast iron as dovetails to interlock stone segments during the construction of the Anji Bridge as shown in Figure 9.1, which is still in use after surviving numerous wars, flood, and earthquakes. Techniques did not improve until the eighteenth century when new scientific and engineering knowledge was more widely known. New construction material, iron, especially the cast iron in mass production, enabled the creation of new bridge systems such as trusses. The world’s first cast iron truss bridge was built in Coalbrookdale, Telford, England, in 1779, shown in Figure 1.2. This bridge is still in use carrying occasional light transport and pedestrians. Modern bridges are the evolution of the early bridges using modern materials, concrete, and steel. With the aid of modern technology, especially after the invention of the computer and the associated computational

tools, bridges can be built with incredible span lengths. Roman viaducts inspired the building of another incredible Roman viaduct structure, Millau Viaduct (Figure 1.3), a cable-stayed bridge in Southern France. It is the tallest bridge in the world with one of the masts standing at 343 m (1125 ft) above the base of the structure. Currently, the longest span bridge in the world (1991 m or 6532 ft) is the Akashi Kaikyo Bridge, a suspension bridge linking the city of Kobe on the mainland of Honshu to Iwaya on Awaji Island, Japan (Figure 1.4).