Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
The Artificial Dialogue Applied to the Professional Sciences - Cicero's Dialogues
Lastly there sprang up in the aesthetic literature of this period the artistic treatment of subjects of professional science in the form of the stylistic dialogue, which had been very extensively in use among the Greeks and had been already employed also in isolated cases among the Romans.(37)
37. Cf. IV. XIII. Sciences
Cicero especially made various attempts at presenting rhetorical and philosophical subjects in this form and making the professional manual a suitable book for reading. His chief writings are the -De Oratore- (written in 699), to which the history of Roman eloquence (the dialogue -Brutus-, written in 708) and other minor rhetorical essays were added by way of supplement; and the treatise -De Republica- (written in 700), with which the treatise -De Legibus- (written in 702?) after the model of Plato is brought into connection. They are no great works of art, but undoubtedly they are the works in which the excellences of the author are most, and his defects least, conspicuous.
The rhetorical writings are far from coming up to the didactic chasteness of form and precision of thought of the Rhetoric dedicated to Herennius, but they contain instead a store of practical forensic experience and forensic anecdotes of all sorts easily and tastefully set forth, and in fact solve the problem of combining didactic instruction with amusement.
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Reference address : https://www.ellopos.net/elpenor/rome/5-12-religion-culture-literature-art.asp?pg=86