The mountain passes in northwestern Pakistan, most notably the Khyber Pass, are the routes taken by peoples who migrate to India.

Although unrecorded migrations may have taken place earlier, it is certain that migrations increased in the second millennium BCE.

The records of these Indo-European speakers are literary, not archaeological: the earliest evidence of the group is from Vedic Sanskrit, the language used in the ancient preserved texts of the Indian subcontinent, the foundational canon of Hinduism known as the Vedas, collections of orally transmitted hymns.

The speakers of Old Indo-Aryan appear in the greatest of these hymns, the Rig Veda, as a tribally organized, pastoral, and pantheistic people.

The Indo-Aryan superstrate in Mitanni, which suggests that an Indo-Aryan elite imposed itself over the Hurrian population in the course of the Indo-Aryan expansion, is of similar age as the Rigveda (and almost identical to it), but the only evidence is a number of loanwords.