Papia in Liguria, commemoratio sancti Severini Boetii, martyris, qui, scientia et ac scriptis præclarus, in carcere detentus tractatum scripsit de consolatione philosophiæ et Deo usque ad mortem a Theodorico rege inflictam cum integritate servivit.
So this is the author of The Consolation of Philosophy. I knew he had been imprisoned, and wrote the book in his cell, but I did not know that he was a saint, let alone a martyr!
Read more here.
The title of martyr seems to have been given him because Theodoric was an Arian: well, there are plenty of other saints in the calendar whose death was only dubiously martyrdom (Edith Stein, for instance: few doubt her virtue and erudition, but she died for her Jewishness, not her Christianity): in Boethius' case, no doubt, the title of saint followed naturally; if a martyr, therefore a saint.