The didactic letters prefacing Marcellus' on drugs as evidence for the expertise and reputation of doctors in the late Roman empire.

The didactic letters prefacing Marcellus's On Drugs are examined. It appears that one reason for writing such didactic letters was to equip the addressee with sufficient knowledge to enable him to avoid consulting a doctor, since there was great dissatisfaction with the quality of service rendered and the fees charged by doctors. The letters in the collection will be shown to represent various levels of healers, from the professional city doctor, to the army doctor, to the educated layman. They will also be scrutinized for evidence of the level of expertise of doctors in the late fourth and fifth centuries. Finally, the evidence will be compared with the criteria set some two centuries earlier by Galen in his blueprint for the examination of physicians.