Lope's metrical address is plainly a remote imitation of Horace's epistle to the Pisos, the model of countless critical codes cast into verse. It is the chief Spanish example of this type, as Boileau's 'Art Poétique' is the chief French example and Pope's 'Essay on Criticism' the chief English example. While most of these Horatian imitations have for their main topic poetry and more especially dramatic poetry, attempts were not lacking to borrow the familiar form for non-literary themes; and as a result there are a host of poems in all the modern tongues on the 'Art of War' and the 'Art of Painting,' on the 'Art of Bookbinding' and on the 'Art of Cookery.' Even so late as the first half of the nineteenth century Samson (of the Comédie-Française) condensed his histrionic advice into riming couplets on the 'Art of Acting.' Most of those imitations of Horace's didactic poem which deal with poetry and the drama borrow from the Latin lyrist not only their method but also much of their material. The supersubtle Italian theorists of the theater were relying on Horace even when they supposed that they were interpreting Aristotle; and these expounders of Horace had elaborated legislative enactments for the theater which were readily accepted by all who desired the purification of the drama. This Classicist code of rules for playwrights was mainly negative; it was made up largely of restrictions upon the poet's freedom; it ordered him to do a few things but it forbad him to do many things. It prescribed the total separation of tragedy and comedy, admitting nothing humorous into the former and excluding everything serious from the latter. It insisted severely upon the austere dignity of tragedy. It told the dramatist to avoid all scenes of violence; and it advised him to use messengers to narrate all events which might not be exhibited with propriety. Above all, it laid stress upon the strict observance of the Three Unities demanding that the playwright should have but one story to set on the stage; that he should show this single action in one place only; and that this single action, shown in a single place, should be begun and completed in a single day.