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
In Rome people were with reason apprehensive as to the destructive
conflagration which was daily spreading. It was resolved next year
(682) to send both consuls against the formidable leaders
of the gang. The praetor Quintus Arrius, a lieutenant of the consul
Lucius Gellius, actually succeeded in seizing and destroying
at Mount Garganus in Apulia the Celtic band, which under Crixus
had separated from the mass of the robber-army and was levying
contributions at its own hand.
But Spartacus achieved
all the more brilliant victories in the Apennines and in northern Italy,
where first the consul Gnaeus Lentulus who had thought to surround
and capture the robbers, then his colleague Gellius and the so recently
victorious praetor Arrius, and lastly at Mutina the governor
of Cisalpine Gaul Gaius Cassius (consul 681) and the praetor Gnaeus
Manlius, one after another succumbed to his blows. The scarcely-
armed gangs of slaves were the terror of the legions; the series
of defeats recalled the first years of the Hannibalic war.