Dux

Until the 3rd century, dux was not a formal expression of rank within the Roman military or administrative hierarchy.[1]

In the Roman army, 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.

In writing his commentaries on the Gallic Wars, Julius Caesar uses the term only for Celtic generals, with one exception for a Roman commander who held no official rank.[2]

By the mid-3rd century AD, it had acquired a more precise connotation defining the commander of an expeditionary force, usually made up of detachments (i.e., vexillationes) from one or more of the regular military formations. Such appointments were made to deal with specific military situations when the threat to be countered seemed beyond the capabilities of the province-based military command structure that had characterised the Roman army of the High Empire.[3]

From the time of Gallienus onwards for more than a century were invariably Viri Perfectissimi, i.e., members of the second class of the equestrian order.[4] Thus, they would have out-ranked the commanders of provincial legions, who were usually Viri Egregii – equestrians of the third class.[5]

Duces differed from praesides who were the supreme civil as well as military authority within their provinces in that the function of the former was purely military. However, the military authority of a dux was not necessarily confined to a single province and they do not seem to have been subject to the authority of the governor of the province in which they happened to be operating. It was not until the end of the 3rd century that the term dux emerged as a regular military rank held by a senior officer of limitanei – i.e. frontier troops as opposed those attached to an Imperial field-army (comitatenses) – with a defined geographic area of responsibility.[note 1]

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 Belgicae secundae ("commander of the second Belgic province") is an example of this office.

After Diocletian's Tetrarchy reform, the provinces were organized into dioceses with each dioceses administered by a vicarius. As with the governors, the vicarius was assisted by a dux. This dux was superior to all other duces within the dioceses—when the vicarius called the legions of the dioceses into action, all of the legions were at the command of the dux. The office of dux was, in turn, made subject to the magister militum of his respective praetorian prefecture, and above him to the emperor. The Dux per Gallias, dux of the diocese of Gaul, is an example of this office.

• In Hong Kong, Scotland, South Africa, Australia and New Zealand dux is a modern title given to the highest-ranking student in academic, arts or sporting achievement (Dux Litterarum, Dux Artium and Dux Ludorum respectively) in each graduating year.[9] This can lead to scholarships at universities.[10] The runner-up may be given the title proxime accessit (meaning "he/she came next") or semidux.[11]
• In Portuguese universities the Dux is the most senior of students, usually in charge of overseeing the praxe (initiation rituals for the freshmen).

• In RuneScape 3, "Dux" is offered to players as a choice of title alongside "Duke" and "Duchess".