Iron is a valuable metal, useful for any kind of tool, but especially for weapons. It is used for knifes and swords, where it is very useful and more durable than bronze. The Bronze Age, the age when bronze was the most common material, ended around 700 BC and was followed by the Iron Age, in which iron became the most important material. The first significant empire based on iron swords was the Roman Empire. But many others followed. The Middle Ages are famous for the knights and their swords. And even modern America's industrial strength rests upon a foundation of iron and its product, steel.
There are various iron ores formed during different geologic processes, and so the mining technology is rather manifold. First man tried to find very rich iron ore, which he could melt with rather low temperatures produced by wood or charcoal. Later the possibilities increased and even ore with a lower grade could be used.
Iron ore was first smelted in bloomeries, the earliest form of smelter capable of smelting iron. They produce a porous mass of iron and slag called a bloom. The bloom contains lumps which are a mix of slag and iron termed sponge iron. Further forged, the quality of the iron increases, and it is now called wrought iron. Later blast furnaces were used, which largely superseded bloomeries and created the much better pig iron.