
The two best-known divisions of Indo-Iranian are Indic (or Indian) and Iranian. In addition another branch, Nuristani (also called the "Kafir" languages), is preserved in pockets of the Himalayas.
The Indo-Iranian group is also called "Aryan", the name used in the ancient literature. Are all Indo-Iranian speakers Aryans because of their common origins? Some handbooks use "Indo-Aryan" to refer to the Indic or Indian subgroup, while other non-Aryan people in the last centuries have used the term for other purposes. Over the millennia, the term "Aryan" has undergone many changes that make its use often ambiguous today.
Indic or Indo-Aryan speakers are often associated with India and the Indus Valley, although speakers of other languages were also in this region in very early times.
Two of the ten most widely spoken languages on earth today, Hindi and Bengali, belong to the Indic branch of Indo-Iranian. The oldest Indic language, Sanskrit, goes back to an oral tradition preserved by the ancestors of Hindu priests, who still speak Sanskrit today.
The sister branch of Indian, Iranian, is represented today by many ancient and modern languages such as Persian, Afghan, and Kurdish. The oldest written Iranian is found in the Old Persian inscriptions of the Achaemenid emperor Darius I, while the teachings of Zarathustra, collected in the Avesta, were passed down orally from preceding centuries by Zoroastrian priests.
In the seventh century BC, the Scythians and Medes joined with the Babylonians to destroy the Assyrian Empire. In the sixth century BC the Persian Achaemenids took over the empire of the Medes and expanded it westward to the shores of Greece and the deserts of Libya. Conquered by Alexander the Great, Persia was then ruled by successive empires.