text: Later developments 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.
  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
  King Arthur, in one of his earliest literary appearances, is described as dux bellorum ("dux of battles") among the kings of the Romano-Britons in their wars against the Anglo-Saxons. A chronicle from St Martin's monastery in Cologne states that the monastery had been pillaged by the Saxons in 778, but that it was rebuilt by an "Olgerus, dux Daniæ" (who may have been the historical person around whom the myth of Ogier the Dane formed), with the help of Charlemagne.