Africa's diverse geography influenced the development of its civilizations. In areas of scant rainfall, settlements arose near lakes or rivers. Trading civilizations along the continent's lengthy coast exchanged ideas and goods with places as far away as Rome and India. Movements of people to find better conditions, such as the Bantu migration, spread culture to other parts of Africa. In West Africa, a series of kingdoms arose and prospered. Many exchanged goods with Arab traders. Contacts with the Middle East led to the spread of Islamic culture through much of Africa. Wealthy city-states along the coast of East Africa exchanged the raw materials of the interior for finished goods from Asia. They also traded in rich deposits of copper and gold from Southern Africa.