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
So this philosophy thoroughly incorporated itself, as a plant
borrowed no doubt from abroad but acclimatized on Italian soil,
with the Roman national economy, and we meet its traces in the
most diversified spheres of action. Its earliest appearance beyond
doubt goes further back; but the Stoa was first raised to full
influence in the higher ranks of Roman society by means of the
group which gathered round Scipio Aemilianus.
Panaetius of Rhodes,
the instructor of Scipio and of all Scipio's intimate friends in
the Stoic philosophy, who was constantly in his train and usually
attended him even on journeys, knew how to adapt the system to
clever men of the world, to keep its speculative side in the
background, and to modify in some measure the dryness of the
terminology and the insipidity of its moral catechism, more
particularly by calling in the aid of the earlier philosophers,
among whom Scipio himself had an especial predilection for the
Socrates of Xenophon.