Trading network, both internal (within the country) and external (foreign), was a significant feature of the urban economy of the Harappans.
Various kinds of metals and precious stones were needed by craftsmen to make goods, but as these were not available locally they had to be brought from outside.
Thus Rajasthan region is rich in copper deposits and the Harappans acquired copper mainly from the Khetri mines located here.
Kolar gold fields of Karnataka and the river-beds of the Himalayan rivers might have supplied the gold.
The source of silver may have been Jwar mines of Rajasthan. It is believed that it must have also come from Mesopotamia in exchange for the Harappan goods.
The Harappans were engaged in external trade with Mesopotamia. It was largely through Oman and Behrain in the Persian Gulf. It is confirmed by the presence of Harappan art facts such as beads, seals, dice etc. in these regions.
The export from Mesopotamia to Harappans included items such as garments, wool, perfumes, leather products and sliver.