Marius, with Sulla out of Rome, had plotted his own return.
During his period of exile Marius had become determined that he would hold a seventh consulship, as foretold by the Sibyl decades earlier.
Quintus Sertorius, after acquiring some reputation in Rome as a jurist and an orator, had begun a military career.
His first recorded campaign was under Quintus Servilius Caepio at the Battle of Arausio, where he showed unusual courage.
Serving under Gaius Marius in 102 BCE, Sertorius had succeeded in spying on the wandering German tribes that had defeated Caepio.
After this success, he had fought at the great Battle of Aquae Sextiae, in which the Teutons were decisively defeated.
In 97 BCE, he had served in Hispania as a military tribune under Titus Didius, winning the Grass Crown.
He had served in 91 as quaestor in Cisalpine Gaul, where he was in charge of recruiting and training legions for the Social War.
During this time he sustained a wound that cost him the use of one of his eyes.
Upon his return to Rome he ran for tribune, but Sulla had thwarted his efforts (for reasons unknown), causing Sertorius to oppose him.
After Sulla forced Marius into exile, and Sulla left Rome to fight Mithridates, violence erupted between the Optimates, led by the consul Gnaeus Octavius, and the Populares, led by the consul Lucius Cornelius Cinna.
Sertorius now declares for Cinna and the Populares.
Though he has a very bad opinion of Marius, he consents to Marius' return upon understanding that Marius comes at Cinna's request and not of his own accord.
By the end of 87 BCE, Marius returns to Rome with the support of Cinna and, in Sulla's absence, takes control of the city.
Marius declares Sulla's reforms and laws invalid and officially exiles Sulla.
After Octavius surrenders Rome to the forces of Marius, Cinna, and Sertorius in 87, Sertorius abstains from the proscriptions his fellow commanders engage in.
Sertorius goes so far as to rebuke Marius, and moves Cinna to moderation, while annihilating Marius' slave army, which had participated in his atrocities.
