This is, so far as I am aware, the earliest notice of the annual celebration of the day of a martyr’s death, a practice which early became so common in the Church. The next reference to the custom is in Tertullian’s de Corona, 3 (cf. also Scorp. 15). So natural a practice, however, and one which was soon afterward universal, need not surprise us at this early date (see Ducange, Natalis, and Bingham, Ant. XIII. 9. 5, XX. 7. 2).