Saint Nicomedes was a Martyr of unknown era, whose feast is observed 15 September.
The Roman Martyrologium and the historical Martyrologies of Bede and his imitators place the feast on this date. The Gregorian Sacramentary contains under the same date the orations for his Mass. The name does not appear in the three oldest and most important Manuscripts of the Martyrologium Hieronymianum, but was inserted in later recensions ("Martyrol. Hieronymianum", ed. G. B. de Rossi-L. Duchesne, in Acta SS., November II, 121). The saint is without doubt a martyr of the Roman Church.
He was buried in a catacomb on the Via Nomentana near the gate of that name. Three seventh century Itineraries make explicit reference to his grave, and Pope Adrian I restored the church built over it (De Rossi, Roma Sotterranea, I, 178-79). A titular church of Rome, mentioned in the fifth century, was dedicated to him (titulus S. Nicomedis).
Nothing is known of the circumstances of his death. The legend of the martyrdom of Saints Nereus and Achilleus introduces him as a presbyter and places his death at the end of the first century. Other recensions of the martyrdom of St. Nicomedes ascribe the sentence of death to the Emperor Maximianus (beginning of the fourth century).