The production of iron began some time in the second millenium BCE in western to central Asia. Its precise history is not clear, but the most recent evidence tells us it could date as far back as 2000 BCE in Anatolia, 1800 BCE in India and 1500 BCE in Africa, suggesting that it arose in various regions independently and was then diffused from these centres, not appearing in Britain for example until it was imported as a new technology around 700 BCE.
Although iron was known to human cultures as early as the second millenium BCE, its mass production was only possible with the invention of the bloomery. This was a furnace capable of achieving the high temperatures required to smelt it. A key impetus to creating this technology was the shortage of copper and tin following the Bronze Age collapse.
Smelting is the process by which iron is extracted from iron ore: the intense temperatures make the iron separate from the rest of the ore in a mass known as a ‘bloom’. The ancient blacksmith would hammer this mass to knock out cinders and slag and produce wrought iron, a hard malleable substance ideal for making tools. In its natural form iron is too soft to be very useful, but when combined with carbon it becomes harder than bronze. The bloomery allowed the controlled absorption of carbon by burning charcoal.
The working of iron also allowed the production of steel, an alloy known to the ancient world in which iron is mixed with carbon. The oldest example we have was found at a site in Turkey: thought to be part of a knife, it dates to around 2000 BCE. Steel has the hardness of cast iron (which has a high carbon content), and the malleability of wrought iron, making it the most useful iron product, but ancient technology could not produce it efficiently. Steel did not displace iron as the dominant material of civilisation until well into the modern era, when the Industrial Revolution introduced new methods for its mass production.
Iron did not sweep instantly across the ancient world, but over the next several centuries it spread at different times into different regions. There is a gap between the dates of the first iron use and the dates that a culture is considered to have entered the Iron Age, i.e. when iron displaced bronze, wood and stone as the principal material for tools and weapons.
Iron had a number of advantages. It was harder than bronze, making it more durable and much more effective for implements, transforming agricultural productivity through the introduction of iron axes and iron ploughs. Even in the Bronze Age, farmers often used wood and stone tools because bronze was not strong enough to work the earth. Iron was also more abundant than bronze, making it cheaper. Bronze was an expensive preserve of the ruling class, used for weapons, statues and luxury goods while the toiling masses remained dependent upon wood and stone. Iron was technology for the masses – every village could support its own blacksmith.
The superiority of iron weapons is sometimes given as a possible cause of the Bronze Age collapse, but it seems that the use of iron was not widespread until a period roughly contemporaneous with or after the collapse. It seems more correct to see the mass production of iron as humanity’s response to the crisis of productivity that had caused such a profound faltering and rolling back of society. The advent of mass-produced iron was a revolutionary forward step for human culture, helping to forge new social relations and forms out of the tottering structures of the Bronze Age. The comparatively limited civilisations of that period, built upon key fertile centres such as the Indus Valley and Mesopotamia, could now be superceded by more expansive ones fuelled by bigger surpluses, productivity and populations: such as Assyria, Persia and Rome.