This was an oral tradition, so do not confuse the language called "sanskrit" with the writing system.
Then, too, Indo-European writing systems are all relatively recent arrivals. The oldest stuff is in Mesopotamia. It was developed by the Sumerians, a nomadic people who ALSO built cities, wrote laws, developed weights and measures, and INVENTED writing.
They were non-Indo-European.
Rune alphabets used for Indo-European languages were actually developed AFTER the Roman alphabet. The ancients knew that to be effective an alphabet must work well with the language which is going to use it for writing. The Greek alphabets drew upon earlier Semitic alphabets, and they, in turn, drew upon Egyptian hieroglypic systems (combination of ideographs and syllabries), and those systems, in turn drew upon the earlier Sumerian system.
The Chinese ideographic writing systems begin with characters not all that different than those used initially by the Sumerians and are believed to have been devised by Sumerians. The earliest written Chinese is in such characters.
Going back a few thousand years, the oldest ideogram systems we can hope to understand are located in the Kola peninsula in Finland and Russia.
These systems are so ancient few of the stories have been derived. A number of them have to do with the day to day life of Sa'ami-like cultures, and tell stories about a fellow probably named Lot who wanders around following reindeer and getting in trouble with people who live in settlements.
Pretty exciting stuff eh!