The earliest mention of marmam is found in the "Rig Veda", where Indra is said to have defeated Vritra by attacking his "marmam" with a vajra. References to marmam are also found in the "Atharva Veda". With numerous other scattered references to vital points in Vedic and epic sources, it is certain that India's early martial artists knew about and practiced attacking or defending vital points. Sushruta (c. 6th century BC) identified and defined 107 vital points of the human body in his "Sushruta Samhita". Of these 107 points, 64 were classified as being lethal if properly struck with a fist or stick. Sushruta's work formed the basis of the medical discipline Ayurveda, which was taught alongside various Indian martial arts that had an emphasis on vital points, such as Varma kalai and Marma adi.