There are actually two groups venerated together on this day - the first group consisting of four soldiers and a second group containing sculptors from Sirmium. The first group, Severus, Serverian, Carpophorus and Victorinus were cornicularii of the army (clerks who managed the legion's paperwork and records) and told to sacrifice to Aesculapius (the god of medicine in Greek mythology). When they refused, they were martyred by Emperor Diocletian and buried in the cemetery of Santi Marcellino e Pietro.
The second group, Claudius, Castorius, Simplicius and Nicostratus were sculptors who were ordered to build a statue of Aesculpaius for a new temple being constructed in Pannonia. They refused both to build the statue and refused to offer sacrifice to the Roman gods when Emperor Diocletian ordered. They were placed alive into lead coffins and thrown into the river in the year 287 AD.
The Martyrs were heavily venerated in England and a church was dedicated to them in Canterbury. Famously, Nanni di Banco built a sculpture depicting the martyrs after being commissioned by the guild of stone and woodworkers leader Maestri di Pietra e Legname. Today that statue can be found in the Orsanmichele in Florence, Italy. The men are venerated as the Patron Saints of stonecutters.