Research points to the possibility of the ancient Saraswati river having had a source in the glacial waters of the Himalayas. The theory states that the Tons river became a tributary of the Yamuna a few thousand years ago following a tectonic event in the Shiwalik range near Sirmaur district of Himachal Pradesh. If this is true, the Tons once ran an independent course somewhat parallel to the Yamuna, running south-west into Haryana where the Yamuna merged into it, and lower down the course into Punjab, where the Sutlej merged into it. This river was then the Saraswati mentioned in the Vedic texts as the greatest of all Indian rivers. However, this is just a theory and is yet to be universally accepted.