St. Euphemia, a virgin of Chalcedon, suffered in the persecution continued by the successors of Diocletian, about the year 307. The Council of Chalcedon was held in her sepulchral church. St. Lucy and Geminianus, two other martyrs who suffered in the same persecution, are commemorated with St. Euphemia.
(Source: The New Roman Missal, Rev. F. X. Lasance)