The three-age Stone-Bronze-Iron system, as proposed in modern times by Christian Jürgensen Thomsen, for classifying and studying ancient societies.

The Stone Age –  a broad prehistoric period characterized by use of  stone to make implements

The Bronze Age – a historical period characterized by the use of bronze, proto-writing, and early features of urban civilization.

The Iron Age–  archaeological era in the protohistory ending with the beginning of the historiographical period. It implies that the production of carbon steel has been perfected to the point where mass production of tools and weapons superior to their bronze equivalents become possible.