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
It was only in a comparatively narrow circle not of men of culture--
for such, strictly speaking, no longer existed--but of men of erudition
that the Greek literature was still cherished even when dead;
that the rich inheritance which it had left was inventoried
with melancholy pleasure or arid refinement of research; and that,
possibly, the living sense of sympathy or the dead erudition
was elevated into a semblance of productiveness. This posthumous
productiveness constitutes the so-called Alexandrinism.
It is essentially similar to that literature of scholars, which,
keeping aloof from the living Romanic nationalities and their vulgar
idioms, grew up during the fifteenth and sixteenth centuries
among a cosmopolitan circle of erudite philologues--as an artificial
aftergrowth of the departed antiquity; the contrast between
the classical and the vulgar Greek of the period of the Diadochi
is doubtless less strongly marked, but is not, properly speaking,
different from that between the Latin of Manutius
and the Italian of Macchiavelli.