Magister militum
Magister militum (Latin for "master of soldiers"; pl.: magistri militum) was a top-level military command used in the later Roman Empire, dating from the reign of Constantine the Great. The term referred to the senior military officer (equivalent to a war theatre commander, the emperor remaining the supreme commander) of the empire. In Greek sources, the term is translated either as strategos or as stratelates.
Later, less formal use of the term[edit]
By the 12th century, the term was being used to describe a man who organized the military force of a political or feudal leader on his behalf. In the Gesta Herwardi, the hero is several times described as magister militum by the man who translated the original Old English account into Medieval Latin. It seems possible that the writer of the original version, now lost, thought of him as the hereward' (Old English: here, lit. 'army' and no: weard, lit. 'guard') – the supervisor of the military force. That this later use of these terms was based on the classical concept seems clear.[25]