The Roman Army A to Z: comitatus

comitatus (m. pl. comitatūs)

A mobile field army of the Late Roman period, established by the time of Constantine and possibly introduced by Diocletian, and divided between infantry, commanded by a magister peditum, and cavalry, under the command of a magister equitum (Acta Max. 2.9; CIL III, 6194; AE 1949, 38). [Southern and Dixon 1996]