This article «A Study of the Books 41-42 of Justin's Epitome of the Philippic History of Pompeius Trogus» is an attempt to determine, through the study of the books 41-42 of the Philippic History of Pompeius Trogus, what kind of knowledge a learned Roman living in Augustus' era had about the Parthians. It deals essentially, once again, with the question of Trogus' sources. The analysis of the text lets appear that Trogus combines informations coming from a Greek work specifi cally dedicated to Parthian history and civilization, probably the Parthica of Apollodorus of Artemita, with elements deriving from Roman observations and with his own personal refl exions. This is true for the historical chapters as well as for the ethnographical ones. In consequence, one should consider this text as expressing Trogus' own vision of the Parthians, and not as simply refl ecting a lost source.