The Iron Bridge, erected in Coalbrookdale, England in 1779, was a feat of engineering since it employed cast iron for the first time. The Industrial Revolution of the nineteenth century provided wrought iron truss systems (an iron alloy with a very low carbon percentage), but they lacked the tensile strength to support heavy loads. Cast iron had the necessary strength, but it cracked when stressed rapidly-for example, when a wagon crossed an iron bridge too quickly. By using both cast and wrought iron, the Coalbrookdale bridge overcame this problem. The Iron Bridge was also an early use of railroads in its construction. Trains could be used to transport raw materials across ponds or streams, thus freeing up labor for other tasks. The bridge was made of three sections: two wrought iron girders and one cast iron arch. It spanned the River Severn about 500 feet long and 30 feet wide and was the longest railroad bridge in Britain at the time it was built. Coalbrookdale is a town in South West Shropshire about 20 miles west of London. The river Severn forms most of the eastern boundary of the town. The name "Coalbrookdale" comes from the English word "coal," which means "fuel for cooking or heating." The area around Coalbrookdale was known for its coal mines until 1875, when the last one closed. Today the town is famous as the location of the Iron Bridge built in 1779.