TheComes Britanniarum (Latin for "Count ofthe Britains") was a military post inRoman Britain with command over the mobilefield army from the mid-4th century onwards. It is listed in theList of Offices as being one of the three commands in Britain, along with theDux Britanniarum and theComes litoris Saxonici.^[1] His troops were the main field army (comitatenses) in Britain and not the frontier guards (limitanei) commanded by the other two.

ArchaeologistsTimothy W. Potter andCatherine Johns believe that theComes Britanniarum led anad hoc force created to deal with a particular situation.^[2] They seem to have been appointed during times of crisis. 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 theComes Britannarum had chief command of Roman military forces in Britain.

The first "Count" in Britain wasGratianus Funarius, the father of emperorValentinian I. He may have commanded a task force ofcomitatenses under emperorConstans during his campaign on the island in the winter of 342–3.^[3]

During theGreat Conspiracy,Count Theodosius, the father of emperorTheodosius I, also served as "Count" in Britain.^[4] A permanent office was created later in the fourth or early fifth century, perhaps byStilicho who withdrew troops from Britain to defend Italy in 402.

According to theNotitia Dignitatum, there was a unit called theEquites Taifali established byHonorius under theComes Britanniarum inBritannia.^[5] This unit may have been the same unit as theEquites Honoriani seniores mentioned around the same time.

According to theList of Offices the count commanded six cavalry and three infantry units, probably a force of no more than 6,000 troops. This small force was charged with supporting the frontier troops in fending off the increasing number of barbarian raids during the period. Some units seem to have been transferred from the Duke of Britain's or Count of the Saxon Shore's armies. The office presumably was extinguished with theRoman withdrawal from Britain by 410.

• Gratianus Funarius
• Count Theodosius
• Magnus Maximus