The mesazōn (Greek: μεσάζων "intermediary") was a high dignitary and official during the last centuries of the Byzantine Empire, who acted as the chief minister and principal aide of the Byzantine emperor.
History and functions 
The term's origins lie in the 10th century, when senior ministers were sometimes referred to as the mesiteuontes (Greek: μεσιτεύοντες), i.e. "mediators" between the Byzantine emperor and his subjects (cf. paradynasteuōn). The title first became official in the mid-11th century, when it was conferred to Constantine Leichoudes, the future Ecumenical Patriarch of Constantinople, Constantine III. In the Komnenian period, it was awarded to senior government officials who functioned as de facto prime ministers, such as the epi tou kanikleiou and the logothetēs tōn sekretōn, but had not yet acquired a permanent and specific function, nor the power that would characterize it in later years. Rather, it was a title bestowed on the principal imperial secretary, who acted precisely as an "intermediary" between the Byzantine emperor and other officials. This reflected the shift of the Byzantine government under the Komnenoi from the old Roman-style bureaucracy to a more restricted, aristocratic ruling class, where government was exercised within the imperial household, as in feudal Western Europe. The office of mesazōn became formally institutionalized in the Empire of Nicaea, where the holder of the mesastikion (as the function had become known), served as the Byzantine Empire's chief minister, coordinating the other ministers. As the Byzantine emperor and historian John Kantakouzenos (r. 1347-1354) records, the mesazōn was "needed by the emperor day and night". This arrangement was inherited by the restored Palaiologan Empire and continued in use until the Fall of Constantinople in May of 1453. The office was also used in the same function in the Byzantine courts of Epirus, Morea, and Trebizond. In the latter case, it acquired the epithet megas ("great").
List of mesazontes 
- Constantine Leichoudes, until 1050.
- Theodore Styppeiotes, under Emperor Manuel I Komnenos (r. 1143–1180).
- John Kamateros, under Emperor Manuel I Komnenos.
- Michael Hagiotheodorites, under Emperor Manuel I Komnenos.
- Theodore Maurozomes, under Emperor Manuel I Komnenos.
- Demetrios Komnenos Tornikes, under Emperor John III Vatatzes (r. 1221–1254).
- Theodore Mouzalon, until 1294.
- Nikephoros Choumnos, 1294–1305, under Emperor Andronikos II Palaiologos (r. 1261–1328).
- Theodore Metochites, 1305–1328, under Emperor Andronikos II Palaiologos.
- Alexios Apokaukos, 1328–1345, under Emperors Andronikos III Palaiologos (r. 1328–1341) and John V Palaiologos (r. 1341–1391).
- Demetrios Kydones, 1347–1354, under Emperor John VI Kantakouzenos (r. 1347–1354); 1369–1383 under Emperor John V Palaiologos; 1391–1396 under Emperor Manuel II Palaiologos (r. 1391–1425).
- George Goudelis, late 1390s under Emperor Manuel II Palaiologos.
- Demetrios Chrysoloras, 1403–1408 in Thessalonica under Emperor John VII Palaiologos.
- George Doukas Philanthropenos, 1430–1439.
- Demetrios Palaiologos Kantakouzenos, 1434/1435–1448 under Emperor John VIII Palaiologos (r. 1425–1448).
- George Doukas Philanthropenos and Manuel Iagaris Palaiologos, 1438–1439, while accompanying Emperor John VIII Palaiologos to Italy.
- Loukas Notaras, 1434–1453, last mesazōn of the Byzantine Empire under Emperors John VIII Palaiologos and Constantine XI Palaiologos (r. 1449–1453).
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