A much more convincing theory than that of the western Iranians having emigrated from North to South across the Caucasus is that of a slow, progressi… - Gherardo Gnoli

[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…” ...

“The fact [is] that Avestan geography, particularly the list in Vd. I, is confined to the east,” ...[this list is] “remarkably important in reconstructing the early history of Zoroastrianism”. ...

Now, the obstacle that arises from the theory of the Medes and the Persians having emigrated from the North ... on the basis of a highly conjectural interpretation of the archaeological evidence, is now removed by the archaeologists themselves. A body of evidence... orients us in quite a different direction, namely towards that of a migratory movement, probably a slow, progressive one, from East to West, along the great Khorasan Road.....