BRIDGESPOTTING

The first use of cast iron for a bridge was at a place now known as the village of Ironbridge, near Coalbrookdale in the Severn Gorge in Shropshire, England. Mass production and use of iron marks the beginning of the Industrial Revolution. Therefore, it is fitting that the first bridge constructed using this new material is located directly in the heart of a UNESCO World Heritage Site established to recognize the birthplace of the Industrial Revolution. Built in 1779, the Iron Bridge still stands and is a major tourist attraction.

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The Iron Bridge is a completely open-spandrel arch structure, with individual structural pieces shaped in pleasing circular, curved, and figure-eight patterns. Another interesting feature of Iron Bridge that attracts tourists is the unusual shape of the arch. The shape of most arches used to construct bridges is flattened, to allow the deck of the bridge to be as level as possible. The higher the arch, the more the deck of the bridge needs to be sloped. This, in turn, requires extra work on the part of horses and people to carry heavy loads up and over the bridge.

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Being the first large-scale use of cast iron, the easiest way to create the curved molds required for the arch of Iron Bridge was to use a pin and string, which generate a perfectly circular shape. Therefore, the deck of Iron Bridge is steeply sloped, which is noticeable when you walk over it. Of more importance to photograph-minded tourists is the reflection of the arch in the Severn River. Because the arch itself is a perfect half-circle, a photograph from the correct angle and time of day generates a beautiful complete circle. Among the many images of the bridge you will find printed on book covers, postcards, T-shirts, and coffee cups in the Ironbridge village shops, you will always find several taken specifically to demonstrate the circle.

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The Iron Bridge was built not only to allow access across the Severn River, but also to advertise the exciting new product being made in the Severn Gorge, which was cast iron. This advertisement was broadcast in gigantic letters on both sides of the bridge, and reads “This Bridge Was Cast at CoalBrook=Dale and Erected in the Year MDCCLXXIX.” The marketing campaign was highly successful, and the Iron Bridge became a tourist attraction almost immediately upon completion.

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I have provided a detailed description of the bridge, and the surrounding Severn Gorge, in my book, Bridgespotting: A Guide to Bridges that Connect People, Places, and Times.