The Harappan civilisation belonged to the Bronze Age. The Bronze Age was the second principal period of the three-age system which began with the Stone Age, followed by the Bronze Age and then the Iron Age. During this phase of human history, bronze and copper were used extensively. Many tools made up of bronze and copper have been discovered from Harappan settlement sites across the subcontinent. This clearly suggests that bronze and copper were the predominant metals used during this period.