Having settled the general fact that the attractive themes of the _romanzi_ should be employed in a perfect heroic poem, we may inquire what particular themes are most fitted to the epic, and what must be the essential qualities of the epic material.[234] In the first place, the subject of the heroic poem must be historical, for it is not probable that illustrious actions such as are dealt with in the epic should be unknown to history. The authority of history gains for the poet that semblance of truth necessary to deceive the reader and make him believe that what the poet writes is true. Secondly, the heroic poem, according to Tasso, must deal with the history, not of a false religion, but of the true one, Christianity. The religion of the pagans is absolutely unfit for epic material; for if the pagan deities are not introduced, the poem will lack the element of the marvellous, and if they are introduced it will lack the element of probability. Both the marvellous and the _verisimile_ must exist together in a perfect epic, and difficult as the task may seem, they must be reconciled. Another reason why paganism is unfit for the epic is to be found in the fact that the perfect knight must have piety as well as other virtues. In the third place, the poem must not deal with themes connected with the articles of Christian faith, for such themes would be unalterable, and would allow no scope to the free play of the poet's inventive fancy. Fourthly, the material must be neither too ancient nor too modern, for the latter is too well known to admit of fanciful changes with probability, and the former not only lacks interest but requires the introduction of strange and alien manners and customs. The times of Charlemagne and Arthur are accordingly best fitted for heroic treatment. Finally, the events themselves must possess nobility and grandeur. Hence an epic should be a story derived from some event in the history of Christian peoples, intrinsically noble and illustrious, but not of so sacred a character as to be fixed and immutable, and neither contemporary nor very remote. By the selection of such material the poem gains the authority of history, the truth of religion, the license of fiction, the proper atmosphere in point of time, and the grandeur of the events themselves.[235]