DUKE (corresponding to Fr. duc, Ital. duca, Ger. Herzog), the title of one of the highest orders of the European nobility, and of some minor sovereign princes. The word "duke," which is derived from the Lat. dux, a leader, or general, through the Fr. duc (O. Fr. dusc, ducs, dus), originally signified a leader, and more especially a military chief, and in this latter sense was the equivalent of the A.S. heretoga (here, an army, and teon, from togen, to draw; Ger. ziehen, zog; Goth, tiuhan; Lat. ducere) and the old Ger. herizog. In this general sense the word survived in English literature until the 17th century, but is now obsolete.
The origin of modern dukes is twofold. The dux first appears in the Roman empire under the emperor Hadrian, and by the time of the Gordians has already a recognized place in the official hierarchy. He was the general appointed to the command of a particular expedition and his functions were purely military. In the 4th century, after the separation of the civil and military administrations, there was a duke in command of the troops quartered in each of the frontier provinces of the empire, e.g. the dux Britanniarum. The number of dukes continually increased, and in the 6th and 7th centuries there were duces at Rome, Naples, Rimini, Venice and Perugia. Gradually, too, they became charged with civil as well as military functions, and even exercised considerable authority in ecclesiastical administration. Under the Byzantine emperors they were the representatives in all causes of the central power. The Roman title of duke was less dignified than that of count (comes, companion) which implied an honourable personal relation to the emperor (see Count). Both titles were borrowed by the Merovingian kings for the administrative machinery of the Frank empire, and under them the functions of the duke remained substantially unaltered. He was a great civil and military official, charged to watch, in the interests of the crown, over groups of several comitatus, or countships, especially in the border provinces. The Sphere of the dukes was never rigidly fixed, and their commission was sometimes permanent, sometimes temporary. Under the Carolingians the functions of the dukes remained substantially the same; but with the decay of the royal power in the 10th century, both dukes and counts gained in local authority; the number of dukes became for the time fixed, and finally title and office were made hereditary, the relation to the crown being reduced to that of more or less shadowy vassalage. (See Feudalism.)
Side by side with these purely official dukedoms, however, there had continued to exist, or had sprung up, either independently or in more or less of subjection to the Frank rulers, national dukedoms, such as those of the Alemanni, the Aquitanians, and, later, of the Bavarians and Thuringians. These were developed from the early Teutonic custom by which the herizog was elected by the nation as leader for a particular campaign, as in the case of the heretogas who had led the first Saxon invaders into Britain. Tacitus says of the ancient Germans reges ex nobilitate, duces ex virtute sumunt; i.e. they elected their dukes for their warlike prowess only, and as purely military chiefs, whereas their kings were chosen from a royal family of divine descent. Sometimes the dukes so chosen succeeded in making their power permanent without taking the style of king. To this national category belong, besides the great German dukedoms, the dukes of Normandy, and the Lombard dukes of Spoleto and Benevento, who traced their origin, not to an administrative office, but to the leadership of Teutonic war bands. With the development of the feudal system the distinction between the official and the national dukedoms was more and more obliterated. By the 13th and 14th centuries the title had become purely territorial, and implied no necessary overlordship over counts and other nobles, who existed side by side with the dukes as tenants-in-chief of the crown. From this time the significance of the ducal title varies widely in different countries. Whenever the crown got the better of the feudal spirit of independence, as in France or Naples, it sank from being a sovereign title to a mere social distinction, implying no political power, and not necessarily any territorial influence. In northern Italy and in Germany, on the other hand, where the crown had proved too weak to combat the forces of disruption, it came ultimately to imply independent sovereignty.
The abolition of the Holy Empire in 1806 removed even the shadow of vassalage from the German reigning dukes, who retain their sovereign status under the new empire. Only one, however, the grand duke of Luxemburg, is now both sovereign and independent. Besides the sovereign dukes in Germany there are certain "mediatized" ducal houses, e.g. that of Ratibor, which share with the dispossessed families of the Italian sovereign duchies certain royal privileges, notably that of equality of blood (Ebenbürtigkeit). In Italy, where titles of nobility give no precedence at court, that of duke (duca) has lost nearly all even of its social significance owing to lavish creations by the popes and minor sovereigns, and to the fact that the title often passes by purchase with a particular estate. Political significance it has none. Some great Italian nobles are dukes, notably the heads of the great Roman ducal families, but not all Italian dukes are great nobles.
In France the title duke at one time implied vast territorial power, as with the dukes of Burgundy, Normandy, Aquitaine and Brittany, who asserted a practical independence against the crown, though it was not till the 12th century that the title duke was definitely regarded as superior to others. At first (in the 10th and 11th centuries) it had no defined significance, and even a baron of the higher nobility called himself in charters duke, count or even marquis, indifferently. In any case the strengthening of the royal power gradually sapped the significance of the title, until on the eve of the Revolution it implied no more than high rank and probably territorial wealth.
There were, under the ancien régime, three classes of dukes in France: (1) dukes who were peers (see Peerage) and had a seat in the parlement of Paris; (2) hereditary dukes who were not peers; (3) "brevet" dukes, created for life only. The French duke ranks in Spain with the "grandee" (q.v.), and vice versa. In republican France the already existing titles are officially recognized, but they are now no more than the badges of distinguished ancestry. Besides the descendants of the feudal aristocracy there are in France certain ducal families dating from Napoleon I.'s creation of 1806 (e.g. ducs d'Albufera, de Montebello, de Feltre), from Louis Philippe (duc d'Isly, and duc d'Audiffret-Pasquier), and from Napoleon III. (Malakoff, Magenta, Morny).
In England the title of duke was unknown till the 14th century, though in Saxon times the title ealdorman, afterwards exchanged for "earl," was sometimes rendered in Latin as dux,  and the English kings till John's time styled themselves dukes of Normandy, and dukes of Aquitaine even later. In 1337 King Edward III. erected the county of Cornwall into a duchy for his son Edward the Black Prince, who was thus the first English duke. The second was Henry, earl of Lancaster, Derby, Lincoln and Leicester, who was created duke of Lancaster in 1351. In Scotland the title of duke was first bestowed in 1398 by Robert III. on his eldest son David, who was made duke of Rothesay, and on his brother, who became duke of Albany.
British dukes rank next to princes and princesses of the blood royal, the two archbishops of Canterbury and York, the lord Chancellor, etc., but beyond this precedence they have no special privileges which are not shared by peers of lower rank (see Peerage). Though their full style as proclaimed by the herald is "most high, potent and noble prince," and they are included in the Almanach de Gotha, they are not recognized as the equals in blood of the crowned or mediatized dukes of the continent, and the daughter of an English duke marrying a foreign royal prince can only take his title by courtesy, or where, under the "house-laws" of certain families, a family council sanctions the match. The eldest son of an English duke takes as a rule by courtesy the second title of his father, and ranks, with or without the title, as a marquess. The other sons and daughters bear the titles "Lord" and "Lady" before their Christian names, also by courtesy. A duke in the British peerage, if not royal, is addressed as "Your Grace" and is styled "the Most Noble." (See Archduke, Grand Duke, and, for the ducal coronet, Crown and Coronet.)
(W. A. P.)
 So Ego Haroldus dux, Ego Tostinus dux, in a charter of Edward the Confessor (1060), Hist. MSS. Comm. 12th rep. app. pt. ix. p. 581.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)