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 expedition of Marius to Capsa was a venture as aimless, as
that of Metellus to Thala had been judicious; but the expedition
to the Molochath, which passed along the border of, if not into,
the Mauretanian territory, was directly repugnant to sound policy.
King Bocchus, in whose power it lay to bring the war to an issue
favourable for the Romans or endlessly to prolong it, now concluded
with Jugurtha a treaty, in which the latter ceded to him a part of
his kingdom and Bocchus promised actively to support his son-in-law
against Rome.
The Roman army, which was returning from the river
Molochath, found itself one evening suddenly surrounded by immense
masses of Mauretanian and Numidian cavalry; they were obliged to fight
just as the divisions stood without forming in a proper order of battle
or carrying out any leading command, and had to deem themselves
fortunate when their sadly-thinned troops were brought into temporary
safety for the night on two hills not far remote from each other.