Ancient Khasi memorial stones, in the East Khasi Hills, in Meghalaya (India)
From reading various old books about the Khasi people ancient funeral traditions, I believe that this is a communal cinerarium (or large burial chamber), where the ashes of the dead were placed.
The site had also many small square structures that look like small burial chamber, i.e. small boxes where the ashes of the dead were kept temporarily before a big ceremony (that did not take place too often) where they were moved into that larger Cinerarium holding the remains of all the Tribe's elders.
For more photos and information about these, go to the Khasi Memorial Stones album (read the album description).