Amid all the disputes and controversies that have centred on the Roman army of the Empire since Mommsen's day, one important chapter in that army's history has remained curiously free from question; however many legions Augustus retained, whenever this legion was raised or that destroyed, all writers are in agreement that Vespasian, early in his principate, cashiered some of the mutinous legions of the Rhine armies.
The great majority of writers are agreed that the legions so dismissed were I, IIII Macedonica, XV Primigenia, and XVI Gallica; though Hardy, following Grotefend and Schilling, suggested that XV might have survived even into Trajan's principate: to-day, however, no one maintains this view, which was the outcome of a failure to account for Vespasian's apparent reduction of the number of legions.