It is well known to many, and will be mentioned more fully in the _Appendix_, that owing to a scarcity of papyrus and parchment, it was customary, at different times, to erase old, in order to admit new, writing. To a MS. of this kind, the name of Palimpsest has been given—a term made use of by Cicero himself. In a letter to the lawyer Trebatius, who had written to him on such a sheet, Cicero says, “that while he must praise him for his parsimony in employing a palimpsest, he cannot but wonder what he had erased to scribble such a letter, except it were his law notes: For I cannot think,” adds he, “that you would efface my letter to substitute your own(457).” This practice became very common in the middle ages, when both the papyrus and parchment were scarce, and when the classics were, with few exceptions, no longer the objects of interest. Montfaucon had remarked, that these obliterated MSS. were perhaps more numerous than those which had been written on for the first time(458). But though in some cases the original writing was still visible on close observation, no practical use was made of such inspection till Angelo Mai published some fragments recovered from palimpsest MSS. in the Ambrosian library, of which he was keeper. Encouraged by his success, he persevered in this new pursuit, and published at intervals fragments of considerable value. At length, being called to Rome as a recompense for his learned labours, Mai prosecuted in the Vatican those noble researches which he had commenced at Milan; and it is to him we now owe the discovery and publication of a considerable portion of Cicero _De Republicâ_, which had been expunged, (it is supposed in the 6th century,) and crossed by a new writing, which contained a commentary by St Augustine on the Psalms(459). The work _De Republicâ_ was begun by Cicero in the month of May, in the year 699, when the author was in the fifty-second year of his age, so that, of all his philosophical writings, it was at least the earliest commenced. In a letter to his brother Quintus, he tells him that he had employed himself in his Cuman and Pompeian villas, in writing a large and laborious political work; that, should it succeed to his mind, it would be well, but, if not, he would cast it into that sea which was in view when he wrote it; and, as it was impossible for him to be idle, commence some other undertaking(460). He had proceeded, however, but a little way, when he repeatedly changed the whole plan of the work; and it is curious to perceive, that an author of so perfect a genius as Cicero, had similar advices from friends, and the same discouragement, and doubts, and irresolution, which agitate inferior writers.