Archaeologists have rediscovered a huge rock art site in southern India where ancient people used boulders to make musical sounds in rituals.
When struck, the impressions emit deep, "gong-like notes"
The Kupgal Hill site includes rocks with unusual depressions that were designed to be struck with the purpose of making loud, musical ringing tones.
It was lost after its discovery in 1892, so this is the first fresh effort to describe the site in over a century.
Details of the research are outlined in the archaeological journal Antiquity.
A dyke on Kupgal Hill contains hundreds and perhaps thousands of rock art engravings, or petroglyphs, a large quantity of which date to the Neolithic, or late Stone Age (several thousand years BC).
Researchers think shamans or young males came to the site to carry out rituals and to "tap into" the power of the site. However, some of it is now at threat from quarrying activities.
The boulders which have small, groove-like impressions are called "musical stones" by locals. When struck with small granite rocks, these impressions emit deep, "gong-like notes".
These boulders may have been an important part of formalised rituals by the people who came there.
Some inscribed pictures date to Neolithic times
In some cultures, percussion plays a role in rituals that are intended for shamen to communicate with the supernatural world. The Antiquity work's author, Dr Nicole Boivin, of the University of Cambridge, UK, thinks this could be the purpose of the Kupgal stones.
The first report of the site was in 1892, in the Asiatic Quarterly Review. But subsequent explorers who tried to find it were unable to do so.
Dr Boivin has been documenting the site. A few pictures of the site were taken in the 19th Century, but the originals were either lost, or allowed to fade.
Many of the motifs on the rocks are of cattle, in particular the long-horned humped-back type found in southern India (Bos indicus).
However, some are of human-like figures, either on their own or with cattle. Some of these in chains, or holding bows and arrows.
The typically masculine nature of the engravings leads Dr Boivin to suggest that the people who made the images were men and possibly those involved in herding cattle or stealing them.
The rock motifs are now under threat from commercial quarrying
The motifs themselves were made by bruising the rocks, presumably with a stone implement.
She believes that the people who made the motifs and those who went to view them must have been physically fit and agile.
Some of the images are in locations so difficult to reach that the artist must have suspended themselves - or got others to suspend them - from an overhang to make the images.
Modern-day commercial granite quarrying has already disturbed some sections of the hill. A rock shelter with even older rock art to the north of Kupgal Hill has been partially destroyed by quarrying.
"It is clear government intervention will be required to elicit effective protection for the majority of the sites in the [area] if these are not to be erased completely over the course of future years," writes Dr Boivin in Antiquity.