MAGISTER OFFICIORUM. – This was one of the great central officials of the absolute Roman Empire, as it took shape following the Diocletianic-Constantinian constitutional reform.
His title almost certainly derives from the fact that he directed the officia or scrinia, i.e., the departments of the imperial chancery. Yet the duties entrusted to him were so numerous and extended across such varied fields that it is difficult to define his office in modern terms. By the late 4th century he already belonged to the highest category of imperial officials, that of the illustres.
The magister officiorum commanded the scholae palatinae, the armed corps that replaced the disbanded praetorian cohorts; he directed the schola of the agentes in rebus publicis, who were charged with supervisory duties concerning public administration; he oversaw the imperial post service and the staff responsible for preparing the emperor’s lodgings and those of his entourage during journeys.
Under his supervision were the arms factories. His department included the officium admissionum, which regulated imperial audiences; thus it fell to him to manage relations with representatives of the Empire’s cities and foreign states, enabling him to influence foreign policy.
He also exercised civil and criminal jurisdiction over all court personnel and, in connection with his oversight of the Empire’s frontiers, jurisdiction over the border troops and their commanders.