Comitatenses is the Latin plural of comitatensis, originally the adjective derived from comitatus ('company, party, suite'; in this military context it came to the novel meaning of 'the field army'), itself rooting in Comes ('companion', but hence specific historical meanings, military and civilian). Comitatus can be: an old Latin word meaning company or retinue or an armed group of men attached to a leader in the Classical Times and in the Middle Ages, a political term used in various meanings: see Comitatus (Classical meaning) in the Middle Ages, the Latin word for county... Comes is the Latin word for companion, either individually or as a member of a collective known as comitatus (compare comitatenses), especially the suite of a magnate, in some cases large and/or formal enough to have a specific name, such as a cohors amicorum. ...

However, historically it became the accepted (substantivated) name for those Roman imperial troops (legions and auxiliary) which were not merely garrisoned at a limes (fortified border, on the Rhine and Danube in Europe and near Persia and the desert tribes elsewhere) — the limitanei or ripenses, i.e. 'along the shores' — but more mobile line troops; furthermore there were second line troops, named pseudocomitatenses, former limitanei attached to the comitatus; palatinae, elite ('guard') units typicaly assigned to Magistri militum; and the scholae of actual palace guards, notably under the magister officiorum, a major court official of the Late Empire. A limes is a Roman wall marking the boundaries of the Roman Empire. ... Limitanei were border guards in the armies of the late Roman Empire. ... Magister militum (Master of the Soldiers) was a rank used in the later Roman Empire dating from the reign of Constantine. ...