The Sarasvati River () is a deified river first mentioned in the Rigveda and later in Vedic and post-Vedic texts. It played an important role in the Vedic religion, appearing in all but the fourth book of the Rigveda. As a physical river, in the oldest texts of the Rigveda it is described as a "great and holy river in north-western India," but in the middle and late Rigvedic books it is described as a small river ending in "a terminal lake (samudra)." As the goddess Sarasvati, the other referent for the term "Sarasvati" which developed into an independent identity in post-Vedic times, the river is also described as a powerful river and mighty flood. The Sarasvati is also considered by Hindus to exist in a metaphysical form, in which it formed a confluence with the sacred rivers Ganges and Yamuna, at the Triveni Sangam. According to Michael Witzel, superimposed on the Vedic Sarasvati river is the heavenly river Milky Way, which is seen as "a road to immortality and heavenly after-life." Rigvedic and later Vedic texts have been used to propose identification with present-day rivers, or ancient riverbeds. The Nadistuti hymn in the Rigveda (10.75) mentions the Sarasvati between the Yamuna in the east and the Sutlej in the west, while RV 7.95.1-2, describes the Sarasvati as flowing to the samudra, a word now usually translated as 'ocean', but which could also mean "lake." Later Vedic texts such as the Tandya Brahmana and the Jaiminiya Brahmana, as well as the Mahabharata, mention that the Sarasvati dried up in a desert. Since the late 19th-century, numerous scholars have proposed to identify the Sarasvati with the Ghaggar-Hakra River system, which flows through northwestern India and eastern Pakistan, between the Yamuna and the Sutlej, and ends in the Thar desert. Recent geophysical research shows that the supposed downstream Ghaggar-Hakra paleochannel is actually a paleochannel of the Sutlej, which flowed into the Nara river, a delta channel of the Indus River. 10,000-8,000 years ago this channel was abandoned when the Sutlej diverted its course, leaving the Ghaggar-Hakra as a system of monsoon-fed rivers which did not reach the sea. The Indus Valley Civilisation prospered when the monsoons that fed the rivers diminished around 5,000 years ago, and ISRO has observed that major Indus Valley civilization urban sites at Kalibangan (Rajasthan), Banawali and Rakhigarhi (Haryana), Dholavira and Lothal (Gujarat) lay along this course. When