River Valley civilisations were characterised by settlements along the rivers and growth of cities which needed, among.other things, stones and wood from distant places to make houses and monuments. Cities also signified that everyone need not depend on land. There was surplus production so that some people could trade or take up other occupations. The surplus had to be traded for goods produced in different pans of the world. For example, we have evidence that Mesopotamians traded extensively with India through Bahrain.
Besides copper, the Indians exported peacocks and apes, ivory and ivory combs, pearls and some textiles. In return, thev received silver and other commodities. Trade, as well as the'desire to control large territories, led to the need for efficient transport. Since the rivers were easy flowing, water transport was most probably developed first.