Cosmas and Damian were twin brothers who lived in Syria during the 200s CE. Under the influence of their devout mother, they embraced the Christian religion that was still outlawed by the Roman authorities. They were both physicians and, unlike colleagues, are said to have provided free treatment. Their growing fame brought them to the attention of the Roman consul, who ordered them to make a sacrifice to the gods. When they refused, they were executed.

Over 48 miracles were credited to the twins, including, amongst others, the development of remedies against plague, scabs, scurvy, kidney stones and bed-wetting. Their most famous miracle involved the alleged replacement of a diseased leg of a white patient with the leg of a recently deceased black man. This legend became increasingly popular from 1200 onwards, and contemporaries would have been in no doubt that it was a miraculous procedure. While amputation was a known, if extreme, procedure, there is no way that a limb from a corpse could have been successfully transplanted to an ailing donor, who then went on to live.

Cosmas and Damian are regarded as saints by the Roman Catholic, Eastern Orthodox and Coptic Christian churches. Roman Catholics consider them the patron saints of medicine and their skulls are venerated as holy relics in a shrine at a church in Madrid. Their saints’ day is 26 September.