Diomedes was a physician of Tarsus in Cilicia, in Asia Minor, who is venerated as one of the Holy Unmercenaries—saints who practiced medicine without taking payment. He studied medicine in his native city and is remembered for treating both bodily and spiritual ailments, using his work among the sick as an occasion to preach the Gospel, leading many to believe in Christ and baptizing them. He is commemorated on August 16.
His zeal as an evangelist carried him beyond his native city. The tradition relates that he traveled to Nicaea in Bithynia, where he continued to heal the sick and to nurture the faith of those he treated. His activity came to the attention of the authorities during the persecution of the emperor Diocletian, who reigned from 284 to 305, and an order was given for his arrest.
By the account preserved in the Orthodox tradition, Diomedes died before he could be brought before the emperor: while he was being taken toward Nicomedia he stepped aside to pray and there gave up his soul to God. The soldiers, finding him already dead, beheaded him so as to demonstrate that they had carried out their orders. He is numbered among the martyrs despite having reposed before his arrest was completed.
A miracle is associated with the soldiers who beheaded him: the tradition relates that they were struck blind, and that their sight was restored only after the severed head had been returned and reunited with the body and they had prayed, whereupon they came to believe in Christ. The Church venerates Diomedes as an Unmercenary Physician, and he is among the saints named during the Mystery of Holy Unction.