4: Sheffield. Archaeologist Julian Richards explores how a small, isolated Yorkshire market town grew to become "steel city". En route he discovers why the town's world-famous cutlery trade has its origins in medieval tools and scythes. He also finds out how the combination of wood and fast-flowing water kick-started the metal-working industries, as well as why that symbol of American frontier life, the bowie knife, was made in Sheffield. Producer John Byrne