The earliest recorded artistic expression of man in India comes from Mohenjo-daro, the Harappan period. It includes steatite seals impressed with diverse animals like the unicorn bull, the Brahmani bull, rhinoceros etc., earthenware jars painted with birds, and stylized flowers, leaves, and terracotta toys, animals and figurines and the occasional copper and stone sculpture. The demise of the Harappan civilization is believed to have been brought about by a major tectonic shift as proved by hydrological studies, which caused wide continuos floods. Following this, came the Aryan culture which is well known for it's Vedic religion. The only Dravidian or Pre-vedic visual art form which survived the test of time was the Cave or Rock paintings which appear to be concentrated in Central India featuring hunting scenes, and sometimes X-ray imagery where internal organs of animals etc. were depicted. These have been dated around c.5500 BC. Historians tend to date the Rigved between 1500 and 1000 BC and the Sama, Yajur and Atharv Vedas between 900 and 600 BC . The most revered of the Indian epics, the Mahabharata (world's longest poem with 90,000 verses) and Ramayana are also believed to have been compiled around 400 BC. The Vedanta and it's texts called the Brahmsutras are attributed to the the first century AD. These are revered and studied in India till date as the basis of modern Hindu intellectualism.