Of the Saint Cyriacus who, together with Saints Largus and Smaragdus and others (of whom Crescentianus, Memmia and Juliana are mentioned in the Roman Martyrology), is venerated on 8 August, all that is known with certainty, apart from their names and the fact of their martyrdom, is that they were buried at the seventh milestone of the Via Ostiensis on that date.
However, legend has it that Cyriacus was a Roman nobleman who converted to Christianity as an adult and, renouncing his material wealth, gave it away to the poor. He spent the rest of his life ministering to the slaves who worked in the Baths of Diocletian. Under the reign of Western Roman Emperor Maximian, co-emperor with Diocletian, Cyriacus was tortured and put to death, beheaded in 303 on the Via Salaria, where he was subsequently buried. With him were martyred his companions Largus and Smaragdus, and twenty others, including Crescentianus, Sergius, Secundus, Alban, Victorianus, Faustinus, Felix, Sylvanus, and four women: Memmia, Juliana, Cyriacides, and Donata.
Saint Cyriacus is credited with exorcizing demons from two girls. The first was Artemisia (or Artemia), the daughter of Emperor Diocletian, which resulted in both Artemisia and her mother Saint Serena converting to Christianity. The second was Jobias, the daughter of Shapur II of Persia (reigned 241-272), which led to the conversion of the King’s entire household. He was bishop of Acona, Italy.