According to these saints' vita in the Acta Sanctorum, St. Peter sent St. Mark to preach the gospel in Aquileia.1 When he had gained a number of conversions and planned to return to Rome, his converts chose one Hermagoras to be his successor and sent him to Rome to be ordained bishop by St. Peter.
When Hermagoras returned to Aquileia he made numerous conversions. This brought him to the attention of Nero, who sent the prefect Sevastus to the city to make him stop. When Hermagoras refused to stop preaching Christ, Sevastus ordered him put in prison. There he performed many miracles. The last straw was his curing a blind woman from a noble family and having her baptized at her home by his archdeacon Fortunatus. For this, the prefect had Fortunatus imprisoned as well, and upon the urging of the pagan priests had both saints beheaded, as in the picture above.
Prepared in 2017 by Richard Stracke, Emeritus Professor of English, Augusta University.
Shown above: The Martyrdom of SS. Hermagoras and Fortunatus, Udine Cathedral (see the description page).