Tell me why most ancient human sites appear in rivers and valleys.

There is water by the river, and it is abundant. Water is what human beings live on.

Drinking: the most basic guarantee of human survival needs

Washing: It can keep clean and keep away from diseases.

Irrigation: Large-scale agriculture can be developed to ensure food supply.

Smelting: the foundation needed for military expansion in the era of cold weapons

Transportation: In ancient times, transportation depended on manpower and animals. When there is a river, there is a boat, which saves more time and effort than manpower and animal power.

Climate: The climate in Okawa is humid and human beings feel very comfortable.

So there is the gathering, reproduction and development of population.