Information about Justin is very scanty. The identification with Justin Martyr is now considered completely groundless. The exact form of his name is in part doubtful: it is impossible to know with certainty whether his nomen gentile was Iunianus or Iunianius. The only two manuscripts (Firenze, bibl. Medicea Laurenziana 66, 21; Città del Vaticano, bibl. Apostolica Vaticana, Latinus 1860) reporting his tria nomina cite them in the genitive (Marci Iuniani Iustini). His work is the only source for his life, but it does not offer many pieces of information which could help placing its author in a specific social, political, and geographical context. We learn from the Preface that he lived, at least for some time, in Rome, where he says he composed the Epitome in moments of otium. He dedicates his work to an unknown person of higher social status. The date is also very uncertain. The oldest quotation from Justin occurs in Jerome (in Dan. prol. 25, 494 Migne), offering the only secure terminus ante quem. Clues inferred from the text of the work do not offer solid evidence, as it is often difficult to know what comes from the epitomiser and what from the author of the original work. Most scholars place him in the second or third century AD; others also suggest the fourth century AD. All these proposals are conjectural.

            Justin epitomises the work of Pompeius Trogus, who is supposed to have written it between the last decade of the first century BC and the first few decades of the first century AD. The little we know about Pompeius Trogus derives from a passage in his historical work (43, 5, 11-12). His family was from Gallia Narbonensis. Pompey the Great granted Roman citizenship to the grandfather of the historian for his services in the war against Sertorius. Other members of the family had a distinguished military career under Roman generals. In particular, the father of the historian acted as head of chancellery under Julius Caesar, one of the highest offices available; the same duty later fell to Aulus Hirtius, consul in 43 BC and one of the closest followers of Caesar. Pliny the Elder states that Pompeius Trogus also wrote a work entitled De animalibus: from the extant fragments it appears to have been an epitome of Aristotle’s zoological treatises rather than an original work. Trogus certainly had a good rhetorical training, as it clearly appears from the only certainly authentic long fragment (38, 4-7, a speech by Mithridates) and, more in general, from the very plan of his work.  [A. Borgna; translation: L. Battezzato]