In enunciating what may be called the ‘five-act rule’ and the ‘three-actor rule’ Horace was prescribing for budding dramatists rather than describing any existing body of drama. Nevertheless the Menander discoveries of the past twenty-five years make it probable that both of these ‘rules’ were in practice observed by the writers of Greek New Comedy, in contrast to the writers of Roman comedy, who observed neither. That the Romans should have abandoned what appears to have been the Greek practice in these two respects is an interesting fact of theatrical history; more importantly it provides us with new avenues for exploring the old question of how much the Romans adapted their Greek originals and for assessing the original contributions of Plautus and Terence.