Rock-cut monuements were begun initially for the Ajivikas patronized first by Asoka, the Mauryan Emperor. Those caves are in the Barabar and Narjuni Hills in Bihar. Since then the Buddhists adopted the medium of rock-cut architecture and continued with the tradition for more than one millenia. Later on the Jains and Hindus also joined the bandwagon and there took lace a great renaissance in the rock-cut architecture of India whose zenith is considered the Great Kalishanath Temple at Ellora. However, due to practicality and feasibilty concerns, I am focussing on the Buddhist corpus only. If the Buddhist corpus is successfully completed, then the Hindu and Jain caves can be considered too.
There is hardly a region in India where rock-cut monuments are not found. However, most of the them were excavated in basalt rock of the Western Ghats of the Deccan plateau in Maharashtra. There are nearly 2500 rock-cut edifices in India only a fragment of which has ever been documented in any medium. There is no such publication that records all the rock-cut monuments of India. Even an inventory does not exist.
These rock-cut monuments have survived the ravages of time; they are much more resilient than the monuments erected in wood, bricks, or stone, which have been perished mostly. The extant monuments have preserved a plethora of evidence for study of the past. They have preserved examples of ancient Indian paintings, sculptures, and a myriad of art and architectural features that give us lots of insight of the wonder that was India.
Ajanta is particularly famous for having preserved some of the oldest examples of painting in the historical period. There are Buddhist narrative paintings: the jatakas, avadanas, and scenes from the life of the Buddha. Many caves have inscriptions in Prakrit and Sanskrit, which attract lots of attention by historians, epigraphist, Indologist, Buddhist scholars, and archaeologists.