Trading network, both internal (within the country) and external (foreign), was a significant feature of the urban economy of the Harappans. As the urban population had to depend on the surrounding countryside for the supply of food and many other necessary products, there emerged a village-town (rural-urban) interrelationship.
Similarly, the urban craftsmen needed markets to sell their goods in other areas. It led to the contact between the towns. The traders also established contacts with foreign lands particularly Mesopotamia where these goods were in demand.
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. The presence of such raw material found at sites away from the place of its origin naturally indicates it must have reached there through an exchange activity.
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.
Among the precious stones used for making beads, the source of lapis-lazuli was located in Badakshan mines in northeast Afghanistan. Turquoise and Jade might have been brought from Central Asia. Western India supplied agate, chalcedony and carnelian. The sea shells must have come from Gujarat and neighbouring coastal areas. Timber of good quality and other forest products were perhaps obtained from the northern regions such as Jammu.
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 artefacts such as beads, seals, dice etc. in these regions. Though the artefacts from those regions are rarely found at the Harappan sites, a seal of West Asian or Persian origin has been discovered at Lothal which confirms this contact.
Mesopotamian cities like Susa, Ur, etc. have yielded about two dozen of Harappan seals. Besides seals, other artefacts of Harappan origin which have been discovered include potteries, etched carnelian beads and dices with Harappan features.
The inscriptional evidence from Mesopotamia also provides us with valuable information on Harappan contact with Mesopotamia. These inscriptions refer to trade with Dilmun, Magan and Meluhha. Scholars have identified Meluhha with Harappan region, Magan with the Makran coast, and Dilmun with Bahrain. They indicate that Mesopotamia imported copper, carnelian, ivory, shell, lapis-lazuli, pearls and ebony from Meluhha.
The export from Mesopotamia to Harappans included items such as garments, wool, perfumes, leather products and sliver. Except silver all these products are perishable. This may be one important reason why we do not find the remains of these goods at Harappan sites.