The main classical Ayurvedic treatises begin with legendary accounts of the transmission of medical knowledge from the gods to sages, and thence to human physicians Thus, the Sushruta Samhita narrates how Dhanvantari, "greatest of the mighty celestials," incarnated himself as Divodāsa, a mythical king of Varanasi, who then taught medicine to a group of wise physicians, including Sushruta himself.
Ayurvedic therapies have varied and evolved over more than two millennia. Therapies are typically based on complex herbal compounds, while treatises written after about 1000 CE introduced mineral and metal substances (perhaps under the influence of early Indian alchemy or rasaśāstra). Ancient Ayurvedic treatises also taught surgical techniques, including rhinoplasty, perineal lithotomy, the suturing of wounds, and the extraction of foreign objects.
