1911 Encyclopædia Britannica/Cohort

COHORT (Lat. cohors), originally a place enclosed: in the Roman army, the name of a unit of infantry. The troops of the first grade, the legions, were divided into cohorts, of which there were ten in each legion: the cohort thus contained 600 men. Among the troops of the second grade (the auxilia) the cohorts were independent foot regiments 500 or 1000 strong, corresponding to the alae, which were similar regiments of cavalry; they were generally posted on the frontiers of the Empire in small forts of four to eight acres, each holding one cohort or ala. The special troops of Rome itself, the Praetorian Guard, the Urbanae Cohortes, and the Vigiles (fire brigade), were divided into cohorts (see further Roman Army). The phrase cohors praetoria or cohors amicorum was sometimes used, especially during the Roman republic, to denote the suite of the governor of a province; hence developed the Praetorian cohorts which formed the emperor’s bodyguard.

In biology, “cohort” is a term for a group of allied orders or families of plants or animals.