Such is the account given by Augustine himself of the occasion and plan of this his greatest work. But in addition to this explicit information, we learn from the correspondence of Augustine, that it was due to the importunity of his friend Marcellinus that this defence of Christianity extended beyond the limits of a few letters. Shortly before the fall of Rome, Marcellinus had been sent to Africa by the Emperor Honorius to arrange a settlement of the differences between the Donatists and the Catholics. This brought him into contact not only with Augustine, but with Volusian, the proconsul of Africa, and a man of rare intelligence and candour. Finding that Volusian, though as yet a pagan, took an interest in the Christian religion, Marcellinus set his heart on converting him to the true faith. The details of the subsequent significant intercourse between the learned and courtly bishop and the two imperial statesmen, are unfortunately almost entirely lost to us; but the impression conveyed by the extant correspondence is, that Marcellinus was the means of bringing his two friends into communication with one another. The first overture was on Augustine's part, in the shape of a simple and manly request that Volusian would carefully peruse the Scriptures, accompanied by a frank offer to do his best to solve any difficulties that might arise in such a course of inquiry. Volusian accordingly enters into correspondence with Augustine; and in order to illustrate the kind of difficulties experienced by men in his position, he gives some graphic notes of a conversation in which he had recently taken part at a gathering of some of his friends. The difficulty to which most weight is attached in this letter, is the apparent impossibility of believing in the Incarnation. But a letter which Marcellinus immediately despatched to Augustine, urging him to reply to Volusian at large, brought the intelligence that the difficulties and objections to Christianity were thus limited merely out of a courteous regard to the preciousness of the bishop's time, and the vast number of his engagements. This letter, in short, brought out the important fact, that a removal of speculative doubts would not suffice for the conversion of such men as Volusian, whose life was one with the life of the empire. Their difficulties were rather political, historical, and social. They could not see how the reception of the Christian rule of life was compatible with the interests of Rome as the mistress of the world. And thus Augustine was led to take a more distinct and wider view of the whole relation which Christianity bore to the old state of things,—moral, political, philosophical, and religious,—and was gradually drawn on to undertake the elaborate work now presented to the English reader, and which may more appropriately than any other of his writings be called his masterpiece or life-work. It was begun the very year of Marcellinus' death, a.d. 413, and was issued in detached portions from time to time, until its completion in the year 426. It thus occupied the maturest years of Augustine's life—from his fifty-ninth to his seventy-second year.