From 113–109 BCE, the Romans suffered a succession of military debacles at the hands of the Cimbrians in Gaul and the Numidians in North Africa. Marius, a parvenu from provincial Arpinum in central Italy, was elected consul in 107 BCE, and under threat of barbarian invasion, instigated far-reaching military reforms. First, he opened the army to the proletariat, who flocked to join, creating a standing army. Next, he divided the army into five classes, of which the crack troops were the principes and the heavy infantry the triarii, flanked and screened in battle by the patrician equites cavalry. The standard battle unit became the cohort, replacing the smaller maniples. Each cohort comprised six centuries, and 10 cohorts (6,000 men) comprised a legion. Non-combatants, from engineers to cooks, comprised 20 per cent of the total strength. In battle, a standard quincunx ‘chequerboard’ formation was adopted, later varied by Caesar to create an ‘open order’ van to maximize flexibility in battle.
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