Iron was used in prehistoric times. Iron has been found in meteorites pure enough to be used without refining. Smelting iron from iron ore has been carried out for at least 5000 years. The first appearance of iron as a building material was in classical Greece, for reinforcing stone lintels and architraves. Uses in cramps, pivots, hinges and locks have been widespread. However, it is only from about the eighteenth century that we have seen more widespread uses for balustrades, balconies, furniture, stairs and various decorative items. The first structural iron girder was manufactured by Charles Bage in 1796 in England, and was used in a five-storey linen mill.

Whilst cast iron contains a large proportion of carbon, steel is an iron product with a carbon content of less than 2%. Towards the end of the nineteenth century steel became a rival to (and gradually replaced) the more brittle cast iron.Whole buildings with a steel structure started to appear then. Today, steel is the only iron-based material used in the building industry. It is possible to use about 20 different alloys in steel, and up to 10 can be used in the same steel. Particularly strong steel is formed by alloying it with small amounts of nitrogen, aluminium, niobium, titanium and vanadium. Normal construction steel such as reinforcing bars, structural elements, wall and roof sheeting does not usually contain alloys. Sheeting products are protected against corrosion by a protective layer of aluminium or zinc. Facing panels in aggressive environments are often made of stainless steel; which is 18% chrome alloy and 8% nickel. By adding 2% molybdenum alloy, an acid-resistant steel can be produced.

As a resource, iron ore is a fairly ‘democratic’ material, being spread quite evenly throughout the world; it is extracted in over 50 countries. Easily available reserves are, however, diminishing rapidly, and some of the alloy metals required (e.g. nickel and zinc) have very limited reserves.

Coal is an important element and generally a prerequisite for the production of cast iron from iron ore. The exception, where the reduction process uses natural gas, requires orewith a very high iron content.

Rock iron ore is extracted by mining; peat bog iron ore is much more accessible and generally the dominant source in earlier times. It lies in loose agglomerations in swamps or bogs. To find it, the bog was probed with a spear or pole. Where there is resistance to the spear, it can be assumed that there is ore. There may even be small traces of iron filings when the pole is removed.