Building on the experience of their BRONZE WORKING, ancient smelters learned IRON WORKING, the manufacture and fabrication of a much more useful metal. Iron ore was extremely common compared to copper and tin, and IRON was harder, less brittle, and could hold a much sharper edge. It was an ideal material for tools and weapons. Some observers consider the development of IRON WORKING to have been a key step in the advance of civilization. It made workers much more efficient and was found useful in many new applications.