Cohortes Britanniarum – The Auxiliary Infantry Cohorts of Britain

Cohors Peditata et Equitata – Auxiliary Infantry and Mixed Cohorts

Auxiliary soldiers were organised in infantry units, cohorts (singular cohors, plural cohortes, abbreviated to coh) and cavalry units, alae (singular ala). Infantry units could also sometimes include a cavalry element (cohors equitata), sometimes described as ‘part-mounted’ regiments. There were two sizes of both cohors and ala, quingenary (quingenaria) and milliary (milliaria), the former with a nominal strength of 500 men, the latter with a nominal strength of 1,000 men, although in practice these figures are different. There were dozens of different auxiliary units based in Britain at any one time. They were made up of cavalry, infantry and mixed units and campaigned and were garrisoned with the legions. Most of the forts of Roman Britain were used by auxiliaries.

The main infantry subdivision of the cohort was the centuria containing 80 men, itself divided into 10 sections (contubernia). The term centuria was often symbolised by an abbbreviation resembling a 7. The main subdivision of the ala or of the cavalry contingent in a cohors equitata was the turma probably consisting of 32 cavalrymen.