The Iron Bridge, Coalbrookdale

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The first bridge in the world built of cast iron, cast at Coalbrookdale under Abraham Darby III and opened across the Severn gorge on New Year's Day 1781. It is an argument in metal rather than an efficient structure: the members are joined with dovetails, mortices and wedges copied straight from carpentry, because nobody yet knew how to detail a cast-iron joint, and it uses far more metal than the span requires. That was the point — it was built to demonstrate publicly that iron could do work reserved for stone and timber, and the demonstration succeeded, iron becoming a structural material for mills, aqueducts and later rails within a generation. The Ironbridge Gorge, including the bridge, the Darby furnace and the surrounding industrial landscape, was inscribed on the UNESCO World Heritage List in 1986.