Magister militum

Magister militum (Latin for "Master of the Soldiers") was a top-level command used in the later Roman Empire, dating from the reign of Constantine.

Used alone, it refers to the senior military officer (equivalent to a war theatre commander, the emperor remaining the formal generalissimo) of the Empire. This Magister Militum was often the power behind the throne and the office was held by Stilicho, Ricimer and others.

The title was often used at a territorial level below each (Western or Eastern) Empire, notably named after a superprovincial unit - pretorian prefecture or Vicarius's diocese in the Tetrarchy tradition - such as the Magister militum per Thracias ("Master of the Soldiers of the provinces in the diocese of the Thraces"), to indicate the commanding general of a large military region.

There was an inevitable devaluation as a result a multiplication of magister commands, such as a division of foot - and mounted troops, under a magister peditum viz. magister equitum, and a special command magister militum praesentalis for the praesentalis ('emperor's own' elite troops).

Compare the usage of "patricius" in the Late Empire.