Plutarch, in Caius Marius, writes:
He was born of parents altogether obscure and indigent, who supported themselves by their daily labor; his father of the same name with himself, his mother called Fulcinia. He had spent a considerable part of his life before he saw and tasted the pleasures of the city; having passed previously in Cirrhaeaton, a village of the territory of Arpinum, a life, compared with city delicacies, rude and unrefined, yet temperate, and conformable to the ancient Roman severity.
However, this tale about Marius' parents and his upbringing is highly unlikely. Adrian Goldworthy, in his book In the Name of Rome : The Men Who Won the Roman Empire, writes that "tales of poverty of 'new men' …must be taken with a pinch of salt." One had to be at least an equestrian to aspire to magistracies in republican Rome, with significant capital at hand. Thus, his family must have been part of the local aristocracy of Arpinum, and influential and powerful no doubt.
Plutarch also says:
"He is said never to have either studied Greek, or to have made use of that language in any matter of consequence; thinking it ridiculous to bestow time in that learning, the teachers of which were little better than slaves."
Goldsworthy's comment on this is that "his education may have been a bit conservative by the standards of the day…"
In other words, Marius was a typical New Man, despised by the Roman aristocracy.