St. Cyriacus was a holy deacon of Rome under Popes Marcellinus and Marcellus. With Largus, Smaragdus, and about 20 others he was crowned with martyrdom in 303, in the persecution of Diocletian. The occasion of the translation of their remains many years later to a church dedicated to them led to the institution of a festival in their memory. St. Cyriacus is invoked for diseases of the eye, and against diabolical possession.
(Source: The New Roman Missal, Rev. F. X. Lasance)