Why was the Tigris and Euphrates Rivers important to ancient Sumerians?

The Tigris and Euphrates Rivers were very important for ancient civilizations because they had water and land for farming, the people who lived on or lived near in the Tigris and Euphrates river can use the river for trading. It was important to Sumerians to get other things from different places, they can also fish in the river and they can plant some crops in the land and use the river to water the crops.