Cyriacus was a Christian deacon living in Rome during the early fourth century. He is remembered as a martyr who died during the Diocletianic Persecution around 303 AD. According to tradition, he was a nobleman who surrendered his wealth to assist the poor and dedicated his life to serving those working in the Baths of Diocletian. He was executed by beheading alongside several companions, including Largus and Smaragdus, during the reign of the Western Roman Emperor Maximian.