Dux

Politics of ancient Rome
Periods
Roman Kingdom 753–509 BC Roman Republic 509–27 BC Roman Empire 27 BC – AD 395 Principate 27 BC – AD 284 Dominate AD 284–641 Western AD 395–476 Eastern AD 395–1453 Timeline
Constitution
Kingdom Republic Sullan republic Empire Augustan reforms Late Empire
Political institutions
Imperium Collegiality Auctoritas Roman citizenship Cursus honorum
Assemblies
Centuriate Curiate Plebeian Tribal
Ordinary magistrates
Consul Praetor Quaestor Promagistrate Aedile Tribune Censor Governor
Extraordinary magistrates
Corrector Dictator Magister equitum Consular tribune Rex Triumviri Decemviri
Public law
Mos maiorum Ius Senatus consultum Quaestio perpetua Senatus consultum ultimum
Titles and honours
Emperor Legatus Dux Officium Praeses Praefectus Vicarius Vigintisexviri Triumvir monetalis Lictor Magister militum Imperator Princeps senatus Pontifex maximus Augustus Caesar Tetrarch
Other countries
v t e

Dux (/dʌks, dʊks/, pl.: ducēs) is Latin for "leader" (from the noun dux, ducis, "leader, general") and later for duke and its variant forms (doge, duce, etc.). During the Roman Republic and for the first centuries of the Roman Empire, dux could refer to anyone who commanded troops, both Roman generals and foreign leaders, but was not a formal military rank.

Roman Empire

Original usage

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

In the

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 they 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]}

The office under the Dominate

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

The title also gave rise to a family name, the aristocratic Doukas clan, which in the 9th–11th centuries provided several Byzantine emperors and generals, while later bearers of the name (maternally descended from the original family) founded the Despotate of Epirus in northwestern Greece.

Post-Roman uses