From the beginning rivers have played an important part in the life of man. Primitive man used rivers as a means of travel. In ancient times, man settled near rivers or on river banks and built up large empires and civilizations. Rome today still stands on both sides of the Tiber. The Menam runs through modern Bangkok, still serving as a great waterway for the transport of goods and people. Water is Nature's most precious gift to man. Man needs water to irrigate his crops, to cook and to wash. In nations far and wide rivers means life and wealth. The Irrawady, Nile, Gangas and a host of other feed and clothe the nation around them. A shortage of water in heavily populated agricultural areas will cause great hardship and starvation as crops fail. Water is also a source of energy and power. Man constructs huge dams across rivers to control the water for irrigation and obtain the energy needed to drive generators. The electrical power is then channeled to homes, cities factories, television stations and the military. Man uses billions of liters of water each day. His main source of water comes from reservoirs which in turn obtain their water from the rivers. Rivers have been important to man ______.