 In the introduction he treats of the form, ornamentation, and iconography of these monuments; he dwells upon the relationship between the sarcophagi of Arles and those of Rome, and the difference between them and those of the south-west of France, in which he finds more distinct signs of local influence.His studies and his personal tastes led him to take an interest also in the history of the persecutions and the martyrs.In numerous writings he treats in particular of the judicial bases of the persecutions and the critical value of the "Acts of the Martyrs".