According to legend, Cosmas and Damian were twin brothers who were doctors. They carried out their healing without payment. They are the patron saints both of the medical profession and of the Medici family of Florence (Medici being the Italian for doctors).
Their precise dates are unknown, but they were martyred at Cyrrhus (Syria), by the Emperor Diocletian, by being beheaded. Several previous attempts to execute them, by throwing them into the sea, by fire, etc., failed. Their most frequently represented miracle is the grafting of a black man's leg on a white man's stump.
They are invariably depicted together wearing the late medieval doctors' garb of red gowns and round hats.