The megas doux (Greek: μέγας δούξ; English: grand duke) was one of the highest positions in the hierarchy of the later Byzantine Empire, denoting the commander-in-chief of the Byzantine navy. It is sometimes also given by the half-Latinizations megaduke or megadux (from Greek μεγαδούξ). The Greek word δούξ is the Hellenized form of the Latin term dux, meaning leader or commander.
History and functions 
The office was initially created by Alexios I Komnenos (r. 1081–1118), who reformed the derelict Byzantine navy and amalgamated the remnants of its various provincial squadrons into a unified force under the megas doux. The Emperor's brother-in-law John Doukas is usually considered to have been the first to hold the title, being raised to it in 1092, when he was tasked with suppressing the Turkish emir Tzachas. There is however a document dated to December 1085, where a monk Niketas signs as supervisor of the estates of an unnamed megas doux. The office of "doux of the fleet" (δούξ τοῦ στόλου), with similar responsibilities and hence perhaps a precursor of the office of megas doux, is also mentioned at the time, being given ca. 1086 to Manuel Boutoumites and in 1090 to Constantine Dalassenos.
John Doukas, the first known megas doux, led campaigns on both land and sea and was responsible for the re-establishment of firm Byzantine control over the Aegean and the islands of Crete and Cyprus in the years 1092–1093 and over western Anatolia in 1097. From this time the megas doux was also given overall control of the provinces of Hellas, the Peloponnese and Crete, which chiefly provided the manpower and resources for the fleet. However, since the megas doux was one of the Empire's senior officials, and mostly involved with the central government and various military campaigns, de factο governance of these provinces rested with the local praitōr and the various local leaders. During the 12th century, the post was dominated by the Kontostephanos family; one of its members, the megas doux Andronikos Kontostephanos was one of the most important officers of Emperor Manuel I Komnenos (r. 1143–1180), assisting him in achieving many land and naval victories.
With the virtual disappearance of the Byzantine fleet after the Fourth Crusade, the title was retained as an honorific in the Empire of Nicaea, where Michael VIII Palaiologos (r. 1259–1282) assumed the title when he became regent for John IV Laskaris (r. 1258–1261). It was also used by the Latin Empire: in 1207 the Latin emperor awarded the island of Lemnos and the hereditary title of megadux to the Venetian Filocalo Navigajoso ("imperiali privilegio Imperii Megaducha est effectus"). His descendants inherited the title and the rule of Lemnos until evicted by the Byzantines in 1278.
After the recovery of Constantinople in 1261, it reverted to its old function as commander-in-chief of the navy, and remained a high rank for the remainder of the empire, its holder ranking sixth after the emperor, between the prōtovestiarios and the prōtostratōr. As such, it was also sometimes conferred upon foreigners in imperial service, the most notable among these being the Italian Licario, who recovered many Aegean islands for Emperor Michael VIII, and Roger de Flor, head of the Catalan Company. After the mid-14th century, the office was sometimes held together with the office of mesazōn, the chief of the imperial secretariat. In this capacity, Alexios Apokaukos served as one of the leading members of the imperial government during the Civil War of 1341–1347, supporting John V Palaiologos (r. 1341–1391) against John VI Kantakouzenos (r. 1347–1354). The last and perhaps most famous megas doux and mesazōn was Loukas Notaras, who served under Constantine XI Palaiologos (r. 1449–1453) until the Fall of Constantinople.
List of known holders 
|John Doukas||1092 – unknown||Alexios I Komnenos||Brother-in-law of Alexios I, previously governor of Dyrrhachium|||
|Landulf||1099–1105||Alexios I Komnenos||Admiral of Western origin|||
|Isaac Kontostephanos||1105–1108||Alexios I Komnenos||Dismissed for his incompetence in the wars against Bohemond|||
|Marianos Maurokatakalon||1108 – unknown||Alexios I Komnenos||Successor of Isaac Konstostephanos|||
|Eumathios Philokales||after 1112 – after 1118||Alexios I Komnenos||previously judicial official in Greece and long-time governor of Cyprus|||
|Constantine Opos||Unknown||Alexios I Komnenos||Distinguished general in the campaigns against the Turks|||
|Leo Nikerites||Unknown||Alexios I Komnenos||Eunuch, previously governor in Bulgaria and the Peloponnese|||
|Nikephoros Vatatzes||Unknown||Alexios I Komnenos (?)||Known only through a seal, possibly dating to the reign of Alexios I|||
|Stephen Kontostephanos||ca. 1145 (?) – 1149||Manuel I Komnenos||Brother-in-law of Manuel I, was killed in office in 1149|||
|Alexios Komnenos||ca. 1155 – after 1161||Manuel I Komnenos||Son of Anna Komnene and Nikephoros Bryennios the Younger|||
|Andronikos Kontostephanos||after 1161 – 1182||Manuel I Komnenos||Manuel's nephew, he was the emperor's most trusted and distinguished general. Blinded by Andronikos I Komnenos in 1182|||
|John Komnenos||Unknown||Manuel I Komnenos||First cousin of Manuel I, son of the sebastokrator Andronikos Komnenos. He fell at Myriokephalon in 1176|||
|Constantine Angelos||Unknown||Isaac II Angelos||Afterwards governor of Philippopolis, he led an unsuccessful usurpation attempt|||
|Michael Stryphnos||ca. 1195 – after 1201/1202||Alexios III Angelos||A favourite of Alexios III. He reportedly sold off the fleet's equipment to enrich himself|||
|Theodotos Phokas||ca. 1210||Theodore I Laskaris||Uncle of Theodore I, emperor of Nicaea, known only from a monastic property deed dating to between 1206 and 1212|||
|Michael Palaiologos||1258||John IV Laskaris||The future Michael VIII, he assumed the office after the murder of George Mouzalon, when he was named regent for the young John IV. He was soon after raised to despotes and eventually to emperor.|||
|Michael Laskaris||1259 – ca. 1272||Michael VIII Palaiologos||Brother of Theodore I, due to his advanced age he never held actual command of the fleet. He held the office until his death|||
|Alexios Doukas Philanthropenos||ca. 1272 – ca. 1275||Michael VIII Palaiologos||Previously protostrator and de facto commander of the fleet since ca. 1263. Held the office of megas doux until his death|||
|Licario||ca. 1275 – unknown||Michael VIII Palaiologos||Italian renegade who entered Byzantine service, he conquered Negroponte and many of the Aegean islands|||
|Roger de Flor||1303–1304||Andronikos II Palaiologos||Leader of the mercenary Catalan Company. He resigned his post in late 1304 favour of his lieutenant, Berenguer de Entença, and was murdered a few months later|||
|Berenguer de Entença||1304–1305||Andronikos II Palaiologos||Roger de Flor's lieutenant and successor as leader of the mercenary Catalan Company. He resigned his office after disagreeing with the emperor|||
|Fernand Ximenes de Arenos||1307/1308 – unknown||Andronikos II Palaiologos||One of the leaders of the Catalan Company, he was named megas doux defected to the Byzantines|||
|Syrgiannes Palaiologos||1321–1322||Andronikos II Palaiologos||One of the main partisans of the young Andronikos III Palaiologos in the Byzantine civil war of 1321–1328, he defected to the aged Andronikos II, who rewarded him with the office of megas doux. After plotting against him as well, he was imprisoned.|||
|Isaac Asanes||unknown – 1341||Andronikos III Palaiologos||Replaced in office by Alexios Apokaukos|||
|Alexios Apokaukos||1341–1345||Andronikos III Palaiologos
John V Palaiologos
|A former partisan and protégé of John Kantakouzenos, Apokaukos was instrumental in the outbreak of the Byzantine civil war of 1341–1347, and until his murder in 1345 led the anti-Kantakouzenist regency for John V|||
|Asomatianos Tzamplakon||ca. 1348||John VI Kantakouzenos||Head of the fleet during the Byzantine–Genoese War of 1348–1349. He died some time before 1356|||
|[Paul?] Mamonas||early 15th century||Manuel II Palaiologos||The Mamonas family were hereditary rulers of Monemvasia|||
|Manuel||unknown – 1410||Manuel II Palaiologos||Mentioned only in an anonymous chronicle as dying of an epidemic in 1410|||
|Paraspondelos||ca. 1437||John VIII Palaiologos||Known only as the father-in-law of Demetrios Palaiologos|||
|Loukas Notaras||after 1441 – 1453||John VIII Palaiologos
Constantine XI Palaiologos
|Notaras served both John VIII and Constantine XI as chief minister, and was executed by the Ottomans after the Fall of Constantinople|||
Cultural references 
In the famous 1490 Valencian epic romance Tirant lo Blanc, the valiant knight Tirant the White from Brittany travels to Constantinople and becomes a Byzantine megadux. This story has no basis in actual history, though it may reflect the above-mentioned cases of the office being conferred upon foreigners.
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