I have a question to Dr Iravatham Mahadevan. Do festivals like PONGAL (TN) or ONAM (Kerala) carry some of those aspects from Indus Valley memory? Because they are not rooted in Religion and origins are obscured from known memory. Submitted by Prakash
The Harappans would have celebrated some festivals. There are seals and sealings showing religious sacrifices, processions etc. but there is no evidence to connect them with the South Indian festival you mention.
See the Cult Object link for another ancient Indus festival scene.
I am quite sure the Harappans celebrated for instance the beginning of the new year at vernal equinox, associating this with the myth of the birth of Murugan (Skanda-Karttikeya). See my book Deciphering the Indus script (1994), p. 205-206, and my paper in Script 1 (2009).