In process known as the Marian reforms, Roman consul Gaius Marius carried out a programme of reform of the Roman military. In 107 BC, all citizens, regardless of their wealth or social class, were made eligible for entry into the Roman army. This move formalised and concluded a gradual process that had been growing for centuries, of removing property requirements for military service. The distinction between the three heavy infantry classes, which had already become blurred, had collapsed into a single class of heavy legionary infantry. The heavy infantry legionaries were drawn from citizen stock, while non-citizens came to dominate the ranks of the light infantry. The army's higher-level officers and commanders were still drawn exclusively from the Roman aristocracy.

Who was now able to join military service in 107 BC?