Three great triads of Ayurveda are:
CHARAKA
The Charaka Samhita is the oldest of the three and was probably first compiled around 1500 BC. It is considered the prime work on the basic concepts of Ayurveda. Charaka represents the Atreya School of physicians. It is a systematic work divided into eight Sthanas or sections, which are further divided into 120 chapters.
SUSHRUTA
Sushruta represents the Dhanwantri School of surgeons, and is considered in Ayurveda to be the father of surgery. Even a great American society of surgeons is named after Sushruta. In the Sushruta Samhita there are sophisticated descriptions of diseases and surgical instruments.
ASHANTANGA HRIDYA
The next important authority in Ayurveda after Charaka and Sushruta is Vagbhatta of Sindh, who flourished about the seventh century AD. His treatise called Ashtanga Hridya.