Such "ritual hearths" are reported from the beginning of the Harappan period itself. It has been suggested that they may have been fire altars , evid… - Bridget Allchin

The orientation of port-holes and entrances on the cist graves is frequently towards the south. [...] This demands comparison with later Indian tradition where south is the quarter of Yama. Among the grave goods, iron is almost universal, and the occasional iron spears and tridents (trisulas) suggest an association with the god Siva. The discovery in one grave of a trident with a wrought-iron buffalo fixed to the shaft is likewise suggestive, for the buffalo is also associated with Yama, and the buffalo demon was slain by the goddess Durgà, consort of Siva, with a trident. [...] The picture which we obtain from this evidence, slight as it is, is suggestive of some form of worship of Siva.

No support for the entry of ‘Aryan’ populations [in India] is found in physical anthropological data (Petraglia & Allchin 2007)

Nomadic herdsmen form an important element of rural life in India and Pakistan today, including the old province of Harappan culture. There is every reason to suppose that they did so in Harappan times, and that they played an important part in the economy and organization of the Harappan world.