The Harappan people traded with the people of Sumer and with the towns lying along the Persian Gulf. Harappan seals and other small objects used by the merchants and traders for stamping their goods have been found in Mesopotamia. The merchandise was shipped from Lothal and incoming goods were received here. Weights and measures which were very accurately graded point to a very high degree of exchange.
Others attribute it to some kind of depression in the land which caused floods. Others point out that the Harappan culture was destroyed by the Aryans but there is hardly any evidence of a mass scale confrontation between the two.