What was the farming method used by the early river valley civilizations?

A river valley civilization is an agricultural nation or civilization situated beside and drawing sustenance from a river. A "civilization" means a society with large permanent settlements featuring urban development, social stratification, specialization of labor, centralized organization, and written or other formal means of communication. A river gives the inhabitants a reliable source of water for drinking and agriculture. Additional benefits include fishing, fertile soil due to annual flooding, and ease of transportation. The first great civilizations, such as those in Mesopotamia, Harappa and Ancient Egypt, all grew up in river valleys. Tigris River flourished near Mesopotamia civilization and river nile flourished near civilization of Egypt

answer; cultural trait;