Sep 15, 2019· T hink of the greatest structures of the 19th century—the Eiffel Tower, the Capitol, the Statue of Liberty—and you'll be thinking of fourth most common element in Earth's crust, iron has been in widespread use now for about 6000 years. Hugely versatile, and one of the strongest and cheapest metals, it became an important building block of the Industrial Revolution, but it's also ...