Comes Britanniarum

[1] His troops were the main field army (comitatenses) in Britain and not the frontier guards (limitanei) commanded by the other two.

Archaeologists Timothy W. Potter and Catherine Johns believe that the Comes Britanniarum led an ad hoc force created to deal with a particular situation.

It appears the title was temporary and did not remain for long, and certainly did not have the permanence of the Dux Britanniarum and the Comes litoris Saxonici, but for the duration of the crisis the Comes Britannarum had chief command of Roman military forces in Britain.

[4] A permanent office was created later in the fourth or early fifth century, perhaps by Stilicho who withdrew troops from Britain to defend Italy in 402.

This small force was charged with supporting the frontier troops in fending off the increasing number of barbarian raids during the period.