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
The subordinate, more individual and ephemeral, species of
historical literature--memoirs, letters, and speeches--were
strongly represented also, at least as respects quantity.
The first statesmen of Rome already recorded in person their
experiences: such as Marcus Scaurus (consul in 639), Publius Rufus
(consul in 649), Quintus Catulus (consul in 652), and even the
regent Sulla; but none of these productions seem to have been of
importance for literature otherwise than by the substance of their
contents.
The collection of letters of Cornelia, the mother of
the Gracchi, was remarkable partly for the classical purity of
the language and the high spirit of the writer, partly as the first
correspondence published in Rome, and as the first literary
production of a Roman lady. The literature of speeches preserved
at this period the stamp impressed on it by Cato; advocates'
pleadings were not yet looked on as literary productions, and such
speeches as were published were political pamphlets.