Our blood itself is part iron. In 1709 James Darby used coke to smelt iron. That led to the widespread commercial use of cast iron. Darby created the Coalbrookdale Ironworks. Then, in 1777, the first delicate iron bridge reached out to span the Severn River at Coalbrookdale.
Cast iron has a wonderful plasticity.
You can cast complex forms cheaply and easily. First we carved those classical stone forms from wood. Then, in 1828, a Philadelphia architect, John Haviland, was designing the Miners' Bank in Pottsville, Pennsylvania. There was no local quarry for stone, so he decided to cast an iron facade in the shape of stone columns and cornices. In 1848 John Bogardus began doing the same thing in downtown New York on a much larger scale.