The aim of the book was twofold: (1) to provide material for professed historians: Hirt. B.G. viii. praef. 5, ‘qui sunt editi, ne scientia tantarum rerum scriptoribus deesset’; (2) to furnish a defence of the author’s own conduct—an object carefully kept in the background. It has been proved that Caesar suppressed facts which would have told against him at Rome (e.g. his rapacity, Sueton. Iul. 54), and the plausible motives which he assigns for some of his actions cannot be accepted as genuine. Cf. the criticism of Asinius Pollio, Sueton. Iul. 56, ‘Pollio Asinius parum diligenter parumque integra veritate compositos putat, cum Caesar pleraque et quae per alios erant gesta temere crediderit, et quae per se vel consulto vel etiam memoria lapsus perperam ediderit, existimatque rescripturum et correcturum fuisse.’ The style is remarkable for its brevity, directness, and the absence of ornament and emotion (Cic. Brut. 262, ‘Nudi sunt, recti et venusti, omni ornatu orationis, tamquam veste, detracto’).
Among the materials used by Caesar in writing the Commentarii were his own despatches to the Senate (ii. 35, iv. 38, vii. 90) and the reports of his legati. Late writers speak of his ἐφημερίδες (e.g. Plut. Caes. 22), but there is no ground for supposing that he kept a regular diary. He depended to a great extent on his own memory (cf. Pollio’s criticism, above).
2. De Bello Civili, in three Books, similar in plan to the Bell. Gall. Book iii. ends abruptly with an event of no great importance, and, as the death of Pompey would have formed a natural ending, we must suppose that Caesar had intended to continue the narrative with the Alexandrian, Spanish, and African wars, but was prevented from carrying out his plan. The work was published after his death, without undergoing revision (Sueton. Iul. 56, ‘Pollio existimat rescripturum et correcturum fuisse’).
Other works in the Corpus Caesarianum.—Sueton. Iul. 56 says, ‘Alexandrini Africique et Hispaniensis [belli] incertus auctor est. Alii Oppium putant, alii Hirtium, qui etiam Gallici belli novissimum imperfectumque librum suppleverit.’
Suetonius evidently believed that Hirtius was the author of B.G. viii., for he introduces a quotation from the preface to that Book with the words, ‘Hirtius ita praedicat’ (ibid.). Hirtius is also mentioned in the MSS. as the author of B.G. viii., and there is no reason to doubt that this is the case. That he is the author of any of the others is rendered doubtful by the fact that his bad health (which lasted to November, B.C. 44) and his position as consul would leave him little time for literature between the death of Caesar (15th March, B.C. 44) and his own death at Mutina (27th April, B.C. 43). Hirtius was thus able to carry out only the first part of the plan sketched in B.G. viii. praef. 2, ‘Caesaris nostri commentarios rerum gestarum, non cohaerentibus superioribus atque insequentibus eius scriptis, contexui, novissimumque imperfectum ab rebus gestis Alexandriae confeci usque ad exitum non quidem civilis dissensionis, cuius finem nullum videmus, sed vitae Caesaris.’
G. Landgraf, Untersuchungen zu Caesar und seinen Fortsetzern (Erlangen, 1888), arrives at the following conclusions:
1. In the Bellum Africum we possess the notes of Asinius Pollio, who took part in the war. That the work partook of the nature of a journal is shown by the style; e.g. interim is used about eighty times as a connecting link, and dates and hours of the day are given carefully. Landgraf supports his position by instancing similarities of expression in the Bell. Afr. and in three letters from Pollio to Cicero (ad Fam. x. 31; 32; 33).
2. Ch. 48-64 of the Bell. Alex. on events in Spain in B.C. 48-7 were sent to Hirtius by Pollio, who was governor of Hispania Ulterior in B.C. 45, and as such was best acquainted with these incidents.
3. On the death of Hirtius, Pollio, on searching for his own papers (which he had lent Hirtius to help him in his work), found Hirtius’ Bell. Gall. viii., and made some additions.
4. The Bell. Civ. was in Hirtius’ possession unedited at his death. Hirtius evidently intended to publish it along with B.G. viii. The third Book had been left unfinished by Caesar, whose notes, some of which were very brief, Hirtius had extended, and filled up the gaps in the narrative. There were also some notes on the Bell. Alex. The Bell. Alex. in the narrower sense (cc. 1-33) Hirtius began with, and in the early chapters contented himself with making small additions. In the later parts are found considerable additions both by Hirtius and by Pollio. Landgraf attempts to distinguish the work of the two: cc. 34-41, on the Bellum Ponticum, being mostly by Pollio, and cc. 65-76, on the wars in Illyria and against Pharnaces, mostly by Hirtius.