The Martyr Diomedes was born in Cilician Tarsus. He was a physician, and a Christian, and he treated not only ills of the body but also of the soul. He enlightened many pagans with belief in Christ, and baptized them. The Church venerates him as a healer and mentions him during the Mystery of Holy Unction.
St Diomedes traveled much, converting people to the true Faith. When he arrived in the city of Nicea, the emperor Diocletian (284-305) sent soldiers to arrest him. Along the way from Nicea to Nicomedia, he got down from the cart so as to pray, and he died.
As proof of carrying out their orders, the soldiers cut off his head, but became blinded. Diocletian gave orders to take the head back to the body. When the soldiers fulfilled the order, their sight was restored and they believed in Christ.
Troparion - Tone 4
Your holy martyr Diomedes, O Lord,
Through his sufferings has received an incorruptible crown from You, our God.
For having Your strength, he laid low his adversaries,
And shattered the powerless boldness of demons.
Through his intercessions, save our souls! SOURCE: