St. Stephen, by birth a Roman, was made Pope on May 3, 253, and governed the Church for three years. He decided the question of the validity of Baptism when administered by heretics, ordering that the tradition should be preserved according to which it was sufficient that they receive confirmation. He was murdered by the Emperor’s soldiers while seated in his Episcopal chair in the catacombs, during the celebration of Mass August 2, 257.
(Source: The New Roman Missal, Rev. F. X. Lasance