Gaius Marius completed his first military service in 134BC

Gaius Marius first enlisted in the military in 134 BC when he joined Scipio Aemilianus' legion on an expedition to Numantia as an officer for the expedition to Numantia. Marius later rose to become one of the most significant figures in Roman history.

When Aemilianus arrived, it is unknown if Marius was already there and working with the previous commander in Numantia. His military prowess caught Scipio Aemilianus' attention while he was serving in the army at Numantia. When the topic of the generals came up during the after-dinner talk and someone questioned Scipio Aemilianus about where the Romans would find a deserving successor, the young Scipio reportedly gave him a gentle pat. Gaius Marius is regarded by Scipio, who is portraying Marius, as a future leader, and this assessment is a precursor to what is to come for Marius. Scipio says: "Perhaps this is the man."

It appears that Marius had aspirations for a political career in Rome from the start of his military career. Marius ran for election as one of the two Forty-four special military courts of the first four corp bodies, according to Plutarch, as a hereditary client of Caecilii Metelli, one of the aristocratic families that were at the time rising as the dominant group in Rome.