To secure his throne and the public tranquillity from these formidable servants, Constantine resolved to divide the military from the civil administration, and to establish, as a permanent and professional distinction, a practice which had been adopted only as an occasional expedient.

The supreme jurisdiction exercised by the Praetorian praefects over the armies of the empire, was transferred to the two masters-general whom he instituted, the one for the cavalry, the other for the infantry; and though each of these illustrious officers was more peculiarly responsible for the discipline of those troops which were under his immediate inspection, they both indifferently commanded in the field the several bodies, whether of horse or foot, which were united in the same army.

Their number was soon doubled by the division of the east and west; and as separate generals of the same rank and title were appointed on the four important frontiers of the Rhine, of the Upper and the Lower Danube, and of the Euphrates, the defence of the Roman empire was at length committed to eight masters-general of the cavalry and infantry.

Under their orders, thirty-five military commanders were stationed in the provinces: three in Britain, six in Gaul, one in Spain, one in Italy, five on the Upper, and four on the Lower Danube; in Asia, eight, three in Egypt, and four in Africa.

The titles of counts, and dukes, by which they were properly distinguished, have obtained in modern languages so very different a sense, that the use of them may occasion some surprise.