Gaius Marius (ca. 157-86 BC) was a Roman general and popular politician. His military reforms and great commands led to the growing involvement of the army in politics and the eventual collapse of the republican system.

Born near Arpinum in central Italy, Marius was of country stock. However, his family was well enough situated that Marius could enter a public career in Rome. He saw his first military service in 134-133 B.C. with Scipio Aemilianus (Scipio Africanus Minor) at Numantia, where Marius was decorated for bravery. Ten years later, as military tribune, he may have served under Q. Caecilius Metellus Balearicus against the Balearic pirates. In 122 Marius returned to Rome to be elected to the quaestorship and may have accompanied Q. Fabius Maximus, son of Scipio Aemilianus, to Gaul.

Marius thus earned powerful backing among the Roman nobility. In consequence, under the patronage of the Metelli, he...