The people of the Indus valley produced and sold goods to cities in nearby regions. They built ships and sent them on the Indus River, which took them out to the Arabian Sea. Their main trading partner was the Mesopotamian civilization. The Indus valley people sent ships filled with their goods to Mesopotamian ports. These ships returned to the Indus valley filled with silver, tin, and copper. The Indus valley people also traded with cities located in the Persian Gulf. Based on the passage, what important role did the Indus River play in the development of the Harappan civilization?