Why did early civilizations arise in the Valleys of the Tigris and Euphrates Rivers?

There were several reasons due to which civilizations arose in the valleys of Tigris and Euphrates rivers. The river banks were fertile and supported a healthy growth of crops. These crops were enough or rather more than enough to support the people of the civilisation. The water of these rivers also had a good amount of marine life, which included fish for eating. These are the basic requirements for supporting a civilization. The rivers also served as a good means of transport. People of those civilization were able to create boats and used the river for transportation.