"of how the young general had outwitted three Marian armies at Auximum"
This is a reference to one of Pompey’s commands, early in his career, against the rebel supporters of Marius
, the popularist leader and enemy of Sulla
. Sulla crushed the populares
power in Rome when he returned from campaigns in the east in 83 BC and set himself up as dictator of Rome. After a civil war in Italy, the remainder of the Marian forces fled.