"...[mandragora is] given for injuries inflicted by serpents and before incisions or punctures are made in the body, in order to insure insensibility to pain. Indeed for this last purpose, for some persons the odour is quite sufficient to induce sleep."
Thus aristocratic Roman author Pliny in Historia Naturalis (c.77AD) describes what would later be known as inhalation anaesthesia. Pliny also relates how smelling the burning skin of a pregnant crocodile could render a patient oblivious of the surgeon's knife; but this notion has not been tested in the modern era.
Refs and Further Reading
Anaesthesia and Anaesthetics