The history of these holy martyrs is very confusing. The Martyrology has this: "At Rome on the Via Lavicana the day of the death of four holy martyrs, the brothers Severus, Severianus, Carpophorus, and Victorinus. Under Emperor Diocletian they were scourged to death with lead rods. Their names were first made known many years later through a divine revelation. As no one knew their names previously, the annual feastday to their honor was celebrated under the title: The Four Crowned Brothers. The designation was retained even after the revelation."
The basilica of the Four Crowned Martyrs also contains the relics of five sculptors who under Diocletian refused to make idols or to venerate sun-god pictures. Reports say they were scourged, placed in lead coffins and submerged in a stream (c. 300). Hagiographers are trying to disentangle the conflicting statements on the relation of these two groups to one another, whether two groups actually existed, whether they were Pannomians or Romans, soldiers or stone-masons, etc.
~from The Church's Year of Grace, Pius Parsch