Aryans created Sanskrit. That’s what the History books say. They apparently put together their own Vedic language and many existing Prakrits (natural languages) like Pali, Maharashtri and Magadhi that were spoken by Dravidians.
At first they just wrote down things that had been handed down orally by their forefathers. Then they translated Dravidian Tamil texts into Sanskrit. That’s supposed to be why Rama and Krishna, both dark-skinned Gods belonging to Tamil lore, have been worshipped all over India for generations, even by people who aren’t descended from Dravidians.
The religion of those times was a mixture of animistic beliefs of the pre-Dravidian tribes, Shiva worship of Dravidians, and Jain teachings that came down from the time of Rishaba, the first tirthankara, who lived about 9000 years ago.
Interestingly, Rama apparently lived around 10,000 B.C., and Krishna around 5000 B.C.; places mentioned in the Ramayana as being forested appear in the Mahabharata as urbanized! However, there are many unproven theories about where Mathura and Dwarka were in Krishna’s time, and the same goes for Lanka in Rama’s time.
There are no architectural remains of Aryan-built cities. One explanation given is that they used only wood for construction. Why would they do that when they had seen what Dravidian technology had achieved? Though they described Dravidians as demons and said other unflattering things about them, they apparently admired their culture enough to translate their literary works into Sanskrit, and adopted quite a lot of their religious beliefs.
Another interesting tidbit I came across is that there was considerable trade between India and the Mediterranean world at this time, both by land and by sea. For example, Hebrew sources mention that the king of Tyre (now in Lebanon) sent a ship to Sophir (their name for South India) every three years to bring back gold, ivory, monkeys, peacocks, sandalwood and precious stones. So the kophim in the Bible is kapi from the Dravidian, and the Greek orydsa, or rice, is the Tamil arisi!