 Of Posidonius's work on tactics, "The Art of War", the Greek historian Arrian complained that it was written 'for experts', which suggests that Posidonius may have had first hand experience of military leadership or, perhaps, utilized knowledge he gained from his acquaintance with Pompey.Posidonius's writings on the Jews were probably the source of Diodorus Siculus's account of the siege of Jerusalem and possibly also for Strabo's.Some of Posidonius's arguments are contested by Josephus in "Against Apion".