The DMP written by Lactantius and published after the 'Edict of Milan' (313), is an unclassifiable book. It was regarded as the first Christian historiography in latin but recent study has defended that the first was really the H.E. by Eusebius which was translated in latin at the end of the IVth century. We have analysed the romantic character of Lactantius' narration through emotional, existential features and its narrative movement. We have compared the prologues of the two books and managed to show that the DMP is surely a Christian history, authentic in many aspects, but discredited in favour of the « canonic » historiography by Eusebius which, even if it contains features of fiction too, is closer to the historic presuppositions of today's readers.