The Roman Legion

node · earth · Frontier provinces, principally Rhine, Danube, Britain, Syria, North Africa

The standing heavy-infantry formation of the imperial army, nominally c. 5,000-6,000 men in ten cohorts, supported by roughly an equal number of non-citizen auxiliaries. After the Marian and Augustan reforms it was a professional long-service force paid from the imperial treasury, which made it simultaneously the guarantor of the frontier and the single largest claim on imperial revenue. Total army strength is a modern reconstruction: commonly given as c. 250,000 under Augustus rising to something like 400,000-450,000 by the early 3rd century, in c. 33 legions plus auxiliary units. These are estimates built from unit lists, not payroll records.