Owing to the illegibility of parts of the Fronto palimpsest and the carelessness of its first editor, Cardinal Mai, it was impossible, even after the critical labours of Niebuhr and his colleagues, to come to any satisfactory conclusion as to the chronology of the Letters. But the edition of S. A. Naber in 1867, which had the advantage of a fresh collation of the MS. by G. N. Du Rieu, further reinforced subsequently by a new examination of the Codex due to W. Studemund, held out a better prospect of success. The labours of C. Brakman in the same direction, published in 1902, have also thrown fresh light upon the subject. Yet the critical world has long been awaiting the appearance of the authoritative recension by Professor E. Hauler of Vienna, who has spent infinite pains over a further, and what may well be a final, inspection of the Codex. A great desideratum, which it is much to be hoped that the new edition will supply, is an exact indication, as far as may be, of the extent of each lacuna in pages, lines, words, or letters. A knowledge of how much is lost in each case is essential for the true understanding of the sequence of thought and time in what remains.