He was martyred about A.D. 258 and was buried not far from the tomb of St. Laurence, where a church was built in his honour.
On the same day, Cassian of Imola, a schoolmaster, was delivered, with his hands tied behind his back, to his young pagan pupils who pierced him to death with their stilettos.
Salus autem justorum a Domino: et protector eorum est in tempore tribulationis. * Noli aemulari in malignantibus: neque zelaveris facientes iniquitatem.
But the salvation of the just if from the Lord: and He is their protector in the time of trouble. * Be not emulous of evildoers; nor envy them that work iniquity.
(Psalm 36:39,1 from the Introit of Mass)
Da, quaesumus, omnipotens Deus: ut beatorum Martyrum tuorum Hippolyti et Cassiani veneranda solemnitas, et devotionem nobis augeat, et salutem.
Grant, we beseech Thee, O almighty God, that this venerable solemnity of Thy holy martyrs Hippolytus and Cassian, may increase our devotion and promote our salvation.
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/07362a.htm