"[the airyo-Sayana refers to] “the vast region that stretches southward from the Hindukus,” ... “from the southern slopes of the great mountain chains towards the valleys of the rivers that flow south, like the Hilmand…” “there is a substantial uniformity in the geographical horizon between Yt.XIX and Yt.X ... and the same can be said for Vd.I … these Avestan texts which contain in different forms, and for different purposes, items of information that are useful for historical geography give a fairly uniform picture: eastern Iran, with a certain prevalence of the countries reaching upto the southern slopes of the Hindukus.” ..."