Gallia Belgica
During the time of the Dominate, the powers of a "dux" were split from the role of the governor and were given to a new office called "dux". The dux was now the highest military office within the province and commanded the legions, but the governor had to authorize the use of the "dux"'s powers. However, once those powers were authorized, the "dux" could act independently from the governor and handle all military matters. The "Dux per Gallia Belgica", dux of the province of "Gallia Belgica", is an example of this office.