[Sidenote: Importance of Cicero’s philosophical works.] To the professional student of ancient philosophy these treatises are of great importance chiefly because of the information they contain concerning the writings and doctrines of Greek philosophers whose works have been lost; to the student of literature they offer admirable examples of learned works in popular form, with all the charm of exquisite literary workmanship; and their influence upon later ages was so great that no one who is interested in the progress of human thought can disregard them. St. Augustine, and many other writers of the early Christian Church, acknowledge their indebtedness to them; they are the foundation of the speculative thought of the middle ages; and it is in great measure due to their influence that the Latin language has remained, almost to our own day, the great medium for the expression of philosophical and scientific speculation. Cicero made “the paths of the noblest learning” accessible not only to his Roman fellow citizens, but to countless generations of men of all lands. His noble purpose was accomplished more grandly than he ever hoped or dreamed. Let those who will, accuse him of shallowness and superficiality; mankind owes him an immeasurable debt of gratitude. Cicero’s orations have served as models for many generations of orators, his rhetorical treatises may be regarded as the foundation of nearly all later theories of style, his philosophical works exerted an influence which permeated the thought of centuries. [Sidenote: Cicero’s letters.] It remains to speak of his letters. These are in some respects the most interesting of his writings, because they show the feelings of the man as he disclosed them to his intimate friends, they make us acquainted with the personal relations between the prominent Romans of the time, and shed many rays of light upon the dark pages of contemporary history. The first of the extant letters is dated in 68 B. C., the last July 28, 43 B. C. The collection was made by Cicero’s friends, and edited probably by his freedman, Tiro, and his publisher and most intimate friend, Atticus. They fall into four groups; sixteen books addressed to various persons (_Ad Familiares_), three books to Cicero’s brother Quintus (_Ad Quintum Fratrem_), sixteen books to Atticus (_Ad Atticum_), and two books to Brutus (_Ad Brutum_). There were originally nine books of letters to Brutus, but only the eighth and the ninth are preserved.