Something of this fear of the horse and of the thundering chariot, the "tank" of the 2nd millennium B.C. is transparent in the famous horse 'Dadhikra… - Michael Witzel

“The Indo-Aryan influence, whether due to actual settlement, acculturation, or, if one prefers, the substitution of Indo-Aryan names for local ones, was powerful enough from early on to replace local names, in spite of the well-known conservatism of river-names. This is especially surprising in the area once occupied by the Indus civilization, where one would have expected the survival of earlier names, as has been the case in Europe and the Near East. At the least, one would expect a palimpsest, as found in New England, with the name of the State of Massachussetts next to the Charles River formerly called the Massachussetts River, and such new adaptations as Stony Brook, Muddy Creek, Red River, etc. next to the adaptations of Indian names such as the Mississippi and the Missouri. The failure to preserve old hydronomes even in the Indus Valley (with a few exceptions noted above) indicates the extent of the social and political collapse experienced by the local population.” (p 107)

Book 5 [...] even knows, in a hymn not suspected as an addition, of the Yamunā.

“A better case for the early linguistic and ethnic history of South Asia can be made by investigating the names of rivers. In Europe river-names were found to reflect the languages spoken before the influx of Indo-European speaking populations. They are thus older than c. 4500-2500 BC (depending on the date of the spread of Indo-European languages in various parts of Europe). It would be fascinating to gain a similar vantage point for the prehistory of South Asia.” (p 104-5)