Why is the Fertile Crescent considered the cradle of civilization?

The Fertile Crescent was framed by two rivers, the Tigris and the Euphrates. These rivers would flood annually, making the soil muddy which in turn would created a layer of silt over the land. Silt was nutritious and beneficial to the harvests which the city depended on. Also, the rivers led to the idea and action of irrigation, which also benefit the growth of crops.