WHY LUCIUS ARTORIUS CASTUS AS DUX WAS NOT A DE FACTO GOVERNOR OF BRITAIN

LAC as dux of British Legionary Vexillations Against Armenia

That Lucius Artorius Castus as dux was also by implication a de facto governor of Britain has been thoroughly discredited.  Yet the idea persists in certain quarters.  While it is undeniable that were he either a legate (something possible for an equestrian to become under special circumstances - even before the time of Commodus) or an acting (i.e. vice) governor he would have claimed such on his stone, the theory has been proposed that a prefect of a legion in the 2nd century could, in fact, have held governing power over the large province of Britain.

To dispense with this notion, I am here quoting from an authoritative discussion of the rank of dux by John F. Hall, Professor of Classics and Ancient History at Brigham Young University ("The Military Reforms of the Emperor Diocletian"): 

"The separation of the military and civil powers was carried to its conclusion under Diocletian. J. G. C. Anderson informs us that

In the later years of Diocletian’s jointreign the principle of divided authority was applied almost universally. By A.D. 304—5 the separation of military and civil functions was normal: only in such

provinces as Mauretania and Isauria, where conditions were disturbed, were the two functions still

combined, and there the combination was permanent.

The military command of the governors was superseded by the creation of a new ofcer—the dux. “The

appointment of an equestrian military ofcer as general commander of the troops of a province or of more than one province, the dux provinciae or dux limitis provinciae,” was “a natural sequel”after the separation of military from civil powers. Jones asserts that “In the system of command Diocletian introduced one innovation, establishing in certain frontier areas zone commanders (duces) distinct from the provincial governors, who retained civil functions only. This change however was farfrom universal: in many areas the provincial governor continued to command the local forces as heretofore.”

The origin of the dux is rightly attributed to Diocletian. The initial existence of the office in the time of his reign is certain. [Emphasis mine.] The first literary mention of Diocletian’s new military commanders occurs in the early part of his reign when the author of the second panegyric refers to those occupying the new ofce of dux as preserving the glory of Diocletian. Regarding this account, Norman H. Baynes explains that “there is no undoubted reference to the later

provincial military commander—the dux—until the year 289.”

The existence of the dux is further attested by several inscriptions dating to the period of the tetrarchy.

Nevertheless, the question may be raised whetherthe dux originated before the time of Diocletian. Duces are mentioned in the passage from Aurelius Victor describing the accession of Diocletian. It may, however, be argued that Aurelius Victor, writing in the late fourth century, applies the terminology of his day to a situation that had existed almost a century before. A further argument forthe early origin of the dux cannot be so easily dismissed, however. An inscription found at Verona, dating to the year 265,records that a certain construction project was undertaken at the direction of one “Aur. Marcellino, v.p., duc. duc.” Mommsen expanded “duc. duc.”into “duce ducenario.”

If his interpretation is correct, the office of dux must have existed, at least in some form, before Diocletian. Baynes attempts to account for the use of the term dux by citing Homo’s argument that Aurelius Marcellinus was not a dux assigned to the command of the troops of a province, but simply a director of a particular project.

Clinton W. Keyes, on the other hand, disagrees with Mommsen’s rendering of “duc. duc.”; as he explains, “the stone-cutter may have repeated these letters by mistake [i.e., duc. duc.], and the man’s title may have been simply v. p. ducenarius, a title which is found in another inscription of a little later date (CIL, III, 1805).”

Of course, there is no good reason to expect a dux limitisto have served at Verona. “It seems much more likely that Marcellinus was a financial officer.”