Iron smelting—the extraction of usable metal from oxidized iron ores—is more difficult than tin and copper smelting. While these metals and their alloys can be cold-worked or melted in relatively simple furnaces (such as the kilns used for pottery) and cast into molds, smelted iron requires hot-working and can be melted only in specially designed furnaces. Iron is a common impurity in copper ores and iron ore was sometimes used as a flux, thus it is not surprising that humans mastered the technology of smelted iron only after several millennia of bronze metallurgy.
The place and time for the discovery of iron smelting is not known, partly because of the difficulty of distinguishing metal extracted from nickel-containing ores from hot-worked meteoritic iron.  The archaeological evidence seems to point to the Middle East area, during the Bronze Age in the 3rd millennium BC. However, wrought iron artifacts remained a rarity until the 12th century BC.
The Iron Age is conventionally defined by the widespread replacement of bronze weapons and tools with those of iron and steel. That transition happened at different times in different places, as the technology spread. Mesopotamia was fully into the Iron Age by 900 BC.  Although Egypt produced iron artifacts, bronze remained dominant until its conquest by Assyria in 663 BC. The Iron Age began in India about 1200 BC, in Central Europe about 800 BC, and in China about 300 BC. Around 500 BC, the Nubians, who had learned from the Assyrians the use of iron and were expelled from Egypt, became major manufacturers and exporters of iron.