The world's first iron bridge was erected 200 years ago by the Quaker iron-master Abraham Darby. It still spans the River Severn, near Coalbrookdale in Shropshire. It was the culmination of 70 years work by the remarkable Darby family which included the invention of coke smelting, the development of the first iron railways, and building some of the earliest steam engines. The Darbys' surprisingly modern approach to their problems lives again as Chronicle shows tub-boats moving along their canal, trolleys climbing their hillside railway, and part of the bridge being specially re-cast in the iron-works that has been on the same site since 1709.