Reference edition:

M. Iuniani Iustini Epitoma historiarum Philippicarum Pompei Trogi; accedunt Prologi in Pompeium Trogum, edidit Otto Seel, Stutgardiae 1985 (Bibliotheca Scriptorum Graecorum et Romanorum Teubneriana).

The Prologi to the Historie Philippicae Pompei Trogi are a kind of summary or index listing the content of the forty-four books of Trogus’ historical work. They are comparable to Livy’s Periochae, even if they are much poorer in content as well as shorter. They probably originated as summaries meant to preface each book of Trogus. They are transmitted as an appendix to Justin’s epitome in  two of the manuscript families of Justin’s text (π and τ). Bongiarius published their first edition in 1581 (Iac. Bongarsii editio Iustini, Parisiis 1581). Their author is unknown. It is difficult to suggest a precise date for their composition, but some elements can be taken into consideration. Scholars suggest that they were written after the epitome, but on the basis of the original work, independently of the epitome. In several cases the prologi mention topics that are absent from the epitome; the prologi are also often at variance with Justin’s criteria and arrangement of topics. It is true that they offer scanty information about the content of Trogus’ work: they invariably start with the formulaic expression primo … secundo … volumine continentur, after which they record very generic and very concise indications about the content of each book. Nonetheless, the prologi are a crucial source for reconstructing the original structure of Trogus’ work.
 [A. Borgna; transl. L. Battezzato]