According to the Charaka tradition, there existed six schools of medicine, founded by the disciples of the sage Punarvasu Ātreya. Each of his disciples, Agnivesha, Bhela, Jatūkarna, Parāshara, Hārīta, and Kshārapāni, composed a Samhitā. Of these, the one composed by Agnivesha was supposed to be the best. The Agnivesha Samhitā was later revised by Charaka and it came to be known as Charaka Samhitā. The Charaka Samhitā was revised by Dridhbala.
Āyurveda is traditionally divided into eight branches which, in Charaka's scheme, are: 1. sūtra-sthāna, general principles; 2. nidāna-sthāna, pathology; 3. vimāna-sthāna, diagnostics; 4. sharīra-sthāna, physiology and anatomy; 5. indriya-sthāna, prognosis; 6. chikitsā-sthāna, therapeutics; 7. kalpa-sthāna, pharmaceutics; and 8. siddhi-sthāna, successful treatment.