The earliest now extant is part of his treatise _De Legibus_, in three books; being a sequel to his work on Politics. Both were written in imitation of Plato's treatises on the same subjects.[216] The latter of these (_De Republica_) was composed a year after the _De Oratore_,[217] and seems to have vied with it in the majesty and interest of the dialogue. It consisted of a series of discussions in six books on the origin and principles of government, Scipio being the principal speaker, but Laelius, Philus, Manilius, and other personages of like gravity taking part in the conversation. Till lately, but a fragment of the fifth book was understood to be in existence, in which Scipio, under the fiction of a dream, inculcates the doctrine of the immortality of the soul. But in the year 1822, Monsignor Mai, librarian of the Vatican, published considerable portions of the first and second books, from a palimpsest manuscript of St. Austin's _Commentary on the Psalms_. In the part now recovered, Scipio discourses on the different kinds of constitutions and their respective advantages; with a particular reference to that of Rome. In the third book, the subject of justice was discussed by Laelius and Philus; in the fourth, Scipio treated of morals and education; while in the fifth and sixth, the duties of a magistrate were explained, and the best means of preventing changes and revolutions in the constitution itself. In the latter part of the treatise, allusion was made to the actual posture of affairs in Rome, when the conversation was supposed to have occurred, and the commotions excited by the Gracchi.