Ferrous metals

Iron ore, the most abundant mineral on our planet, is heavy, metallic in colour, magnetic and rusts.
Ancient Chinese used cast iron in tools and weapons.
By the 1800's, cast iron was being used to build towers and bridges.

Unfortunately, cast iron cracks easilly.  When subjected to vibrations, the metal fatigues.  The structure weakens and may fail.
Tay River bridge collapse 1854

Modern steel is made by a process known as smelting.