The Hilmand region and the Hamun-i Hilmand are beyond all doubt the most minutely described countries in Avestan geography. ... - Gherardo Gnoli

Having done away with the obstacle provided by the theory of the trans-Caucasian migration..., we can see both these peoples as western branches of those same Airyas that in the Younger Avesta are described as being settled in such a large part of the eastern Iranian world....

[This region is subject to] “a process of spiritualization of Avestan geography … in the famous celebration of the Hilmand in the Zamyad Yast…”, and “this pre-eminent position of Sistan in Iranian religious history and especially in the Zoroastrian tradition is a very archaic one that most likely marks the first stages of the new religion … the sacredness of the Hamun-i Hilmand goes back to pre-Zoroastrian times…” ...

“With Varana and Ranha, as of course with Hapta Handu, which comes between them in the Vd. I list, we find ourselves straight away in Indian territory, or, at any rate, in territory that, from the very earliest times, was certainly deeply permeated by Indo-Aryans or Proto-Indoaryans.” ...