The Persians, the Medes and most of the other peoples of ancient Iran belonged to the Iranian race of "Aryan" (Indo-European) origin; which, in other words, means that it was a branch of the Indo-European group. The time of their settlement in Iran is not known, but there is ample evidence to show that the region northwest of Mesopotamia had been inhabited in the fourteenth century B.C. by the Mitannian people, whose kings had Indo-Iranian names, and who worshipped Indo-Iranian gods.
The primitive Iranian language was closely connected with Sanskrit. It has two dialects; first, the "ancient Persian" — the speech of Fars or Persian proper — which is the language of Achaemenid inscriptions; second, the Zend, representing a speech of Media, which was the language of the Mazdean Bible, the Avesta. A more recent form of the Iranian was Pehlevi, the language of the Parthians and Sassanians.