Which is true of mesopotamia? people in mesopotamia relied on irrigation because the tigris and euphrates rivers were too small and unreliable in the desert area. mesopotamia was the second great civilization in the area between the tigris and euphrates rivers. one of the world’s earliest civilizations, mesopotamia believed that all citizens must obey the same set of laws. hammurabi brought the first settlers into the area of the tigris and euphrates rivers and created the civilization of mesopotamia.