furnace but to melt iron I believe would require modern technologies like blast furnaces and electric arc furnaces. What did they do?
Blast furnaces and arc furnaces are modern methods to refine metal quickly, but the ancients didn't have to work that quickly to work iron. That is almost like asking, how did people cook before microwave ovens. These days, such emphasis is put on racing faster than anyone else, to produce something and if you cannot outstrip competition, the work should be abandoned, is the attitude. With bellows and other fans, charcoal ovens produced sufficient heat to make iron. Ancient Africans did this back around 1800 B.C. From then and there iron use spread southerly and over to India, Asia and to the rest of the world.
One answer is that they didn't actually melt iron. possibly by accident, they discovered that hot coal would produce a malleable metal material from certain rocks (most probably 'bog iron ore, or limonite - iron hydroxide). The carbon in the coal acts as a reducing agent, producing carbon dioxide and leaving iron. However, early furnaces did not produce molten iron, but instead produced a squishy, malleable soft material that could be beaten into shape. Because mineral impurities were not removed, the result was a mixture of iron, slag, and carbon. This is a form of wrought iron: extremely durable and hard, but not easily shaped, or able to produce a sharp edge. Early iron was probably inferior to bronze for weapons metal working, until the chinese discovered low-carbon steel, as another answerer noted.
They had clay furnaces, and air bellows. The furnaces were heated with charcoal, which produces a much higher temperature than wood. This was enough to get the right heat during the Iron Age, before they started adding other things to make the various grades of steel.
