Historians differ as to whether the Elamites could be considered "Iranian". On the one hand, the Elamites spoke a non-Iranian language and were culturally closer to the established civilizations of Sumer and Akkad than they were to the tribes of the Iranian plateau. On the other hand, the Elamites linked the old civilizations of Mesopotamia and the new peoples of the plateau, and their version of Mesopotamian civilization was a formative influence on the first indisputably Persian empire of the Achaemenids.