Dux - Roman Empire

Roman Empire

Until the 3rd century, dux was not a formal expression of rank within the Roman military or administrative hierarchy.

In the Roman military, a Dux would be a general in charge of two or more legions. While the title of Dux could refer to a consul or imperator, it usually refers to the Roman governor of the provinces. As the governor, the Dux was both the highest civil official as well as the commander-in-chief of the legions garrisoned within the province.

However, 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 still the highest military office within the province and commanded the legions, but the governor had to authorize the use of the Dux's powers. But once authorized, the Dux could act independently from the governor and handled all military matters. An example would be the Dux per Gallia Belgica who was the Dux of the province of Gallia Belgica.

From Diocletian's Tetrarchy reform, the provinces were organized into dioceses each administered by a vicarius. As with the governors, the vicarius was assisted by a Dux. This Dux was superior to all of other Duces within the dioceses and when the vicarius called the legions of the dioceses into action, all of the legions were at the Dux's command. An example would be the Dux per Gallia who was the Dux of the dioceses of Gaul. The office of Dux was, in turn, made subject to the Magister Militum of his respective Praetorian prefecture, and above him to the emperor.

In the Byzantine era of the Roman Empire, the position of Dux survived (Byzantine Greek: "δούξ", doux, plural "δούκες", doukes) as a rank equivalent to a general (strategos). In the late 10th and early 11th centuries, a doux or katepano was in charge of large circumscriptions consisting of several smaller themata and of the professional regiments (tagmata) of the Byzantine army (as opposed to the largely militia-like forces of most themata). In the Komnenian period, the title of doux replaced altogether the strategos in designating the military official in charge of a thema. In the Byzantine navy, doukes of the fleet appear in the 1070s, and the office of megas doux ("grand duke") was created in the 1090s as the commander-in-chief of the entire navy.