world. However, according to , the probable homeland of Avestan is, in fact, the area south of the Aral Sea. Geographical location of Rigvedic rivers The geography of the Rigveda seems to be centered on the land of the seven rivers. While the geography of the Rigvedic rivers is unclear in some of the early books of the Rigveda, the Nadistuti sukta is an important source for the geography of late Rigvedic society. The Sarasvati River is one of the chief Rigvedic rivers. The Nadistuti sukta in the Rigveda mentions the Sarasvati between the Yamuna in the east and the Sutlej in the west, and later texts like the Brahmanas and Mahabharata mention that the Sarasvati dried up in a desert. Scholars agree that at least some of the references to the Sarasvati in the Rigveda refer to the Ghaggar-Hakra River, while the Afghan river Haraxvaiti/Harauvati Helmand is sometimes quoted as the locus of the early Rigvedic river. Whether such a transfer of the name has taken place from the Helmand to the Ghaggar-Hakra is a matter of dispute. Identification of the early Rigvedic Sarasvati with the Ghaggar-Hakra before its assumed drying up early in the second millennium would place the Rigveda BCE, well outside the range commonly assumed by Indo-Aryan migration theory. A non-Indo-Aryan substratum in the river-names and place-names of the Rigvedic homeland would support an external origin of the Indo-Aryans. However, most place-names in the Rigveda and the vast majority of the river-names in the north-west of the Indian subcontinent are Indo-Aryan. Non-Indo-Aryan names are, however, frequent in the Ghaggar and Kabul River areas, the first being a post-Harappan stronghold of Indus populations. Textual references to migrations Rigveda Just as the Avesta does not mention an external homeland of the Zoroastrians, the Rigveda does not explicitly refer to an external homeland or to a migration. Later Hindu texts, such as the Brahmanas, Mahabharata, Ramayana, and Puranas, are centered in the Ganges region (rather than Haryana and Punjab) and mention regions still further to the south and east, suggesting a later movement or expansion of the Vedic religion and culture to the east. There is no clear indication of general movement in either direction in the Rigveda itself; searching for indirect references in the text, or by correlating geographic references with the proposed order of composition of its hymns, has not led to any consensus on the issue.