Roman Legion Mechanics: Quincunx Lines, the Signifer's Bank, Fustuarium

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In 55 BC Caesar's fleet stalled off Britain until the aquilifer of the 10th Legion leapt into the surf with the eagle, and the troops followed rather than lose it. That reflex was centuries in the making. Early Rome armed its citizens by wealth under the Servian census, but after the Gauls sacked the city following the Allia in 387 BC it reorganized by age and experience: young hastati in front, principes behind, veteran triarii kneeling at the rear, spaced in a quincunx so lines could pass through each other. The professional legion of about 5,000 men was built from eight-man tent groups, centuries under 60 centurions, and immunes such as engineers, clerks and medics.

Each century's signifer carried both the standard and the unit's savings and burial fund, tying every soldier's money to the rallying point. Pay of 225 denarii a year, loot and a retirement of about 3,000 denarii or frontier land sat beside the fustuarium, death by beating at the hands of comrades, and decimation. Once Marius, Sulla and Caesar paid their own men, loyalty shifted from Senate to general, and Augustus answered with 28 legions on the frontiers, pay from the treasury and the imaginifer bearing his likeness. The legions also copied freely, from the Iberian gladius to a beached Carthaginian quinquereme.

• The Roman phrase ad triarios redisse, falling back on the triarii, meant reaching a last resort.
• Each tent group shared a leather tent, a millstone for grinding grain and a pack mule.
• The primus pilus, the senior centurion of the first cohort, often retired into the Roman nobility.
• After Arminius destroyed the 17th, 18th and 19th legions under Varus in 9 AD, those numbers were never used again.
• Montesquieu credited Rome's rise to its readiness to drop its own practices for better ones taken from enemies.